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DICTIONARY 

OF 

ELECTRICAL  WORDS,  TERMS 
AND  PHRASES. 

BY 

EDWIN  J.  HOUSTON,  A.  M., 

Professor  of  Natural  Philosophy  and  Physical  Geography  in  the  Central  High 

School  of  Philadelphia ;  Professor  of  Physics  in  the  Franklin  Institute 

of  Pennsylvania  ;   Electrician  of  the  International 

Electrical  Exhibition,  etc. 


NEW  YORK: 

THE  W.  J.  JOHNSTON  COMPANY,  LD., 
TIMES  BUILDING. 


LONDON : 

- -TIIK  ELECTRICIAN"  PRINTING  AND  PUBLISHING  CO.,  LD., 
1  SALISBURY  COURT,  FLEET  STREET,  E.  C. 


ExLdbrf*  , 
C.  K.  OGDEN 


COPYRIGHT,  1889, 

BY 
THE  W.  J.  JOHNSTON  Co.,  LD. 


r>     r  LIBRARY 

UNIVERSITY  OF  CMTJFORNIA' 
Q.C  SANTA  BARBARA 

505 


PREFACE. 


The  rapid  growth  of  electrical  science,  and  the  almost 
daily  addition  to  it  of  new  words,  terms  and  phrases, 
coined,  as  they  too  frequently  are,  in  ignorance  of  those 
already  existing,  have  led  to  the  production  of  an 
electrical  vocabulary  that  is  already  bewildering  in  its 
extent.  This  multiplicity  of  words  is  extremely  dis- 
couraging to  the  student,  and  acts  as  a  serious  obstacle 
to  a  general  dissemination  of  electrical  knowledge,  for 
the  following  reasons : 

1.  Because,  in  general,  these  new  terms  are  not  to  be 
found  even  in  the  unabridged  editions  of  dictionaries. 

2.  The  books  or  magazines,  in  which  they  were  first 
proposed,  are  either  inaccessible  to  the  ordinary  reader, 
or,  if  accessible,  are  often  written  in  phraseology  unin- 
telligible except  to  the  expert. 

3.  The  same  terms  are  used  by  different  writers  in 
conflicting  senses. 

4.  The  same  terms  are  used  with  entirely  different 
meanings. 

5.  Nearly  all  the  explanations  in  the  technical  dic- 
tionaries are  extremely  brief  as  regards  the  words,  terms 
and  phrases  of  the  rapidly  growing  and  comparatively 
new  science  of  electricity. 

In  this  era  of  extended  newspaper  and  periodical  pub- 
lication, new  words  are  often  coined,  although  others, 


n  PREFACE. 

already  in  existence,  are  far  better  suited  to  express  the 
same  ideas.  The  new  terms  are  used  for  a  while  and 
then  abandoned;  or,  if  retained,  having  been  imperfectly 
defined,  their  exact  meaning  is  capable  of  no  little 
ambiguity ;  and,  subsequently,  they  are  often  unfortun- 
ately adopted  by  different  writers  with  such  varying 
shades  of  meaning,  that  it  is  difficult  to  understand 
their  true  and  exact  significance. 

Then  again,  old  terms  buried  away  many  decades  ago 
and  long  since  forgotten,  are  dug  up  and  presented  in 
such  new  garb  that  their  creators  would  most  certainly 
fail  to  recognize  them. 

It  has  been  with  a  hope  of  removing  these  difficulties 
to  some  extent  that  the  author  has  ventured  to  present 
this  Dictionary  of  Electrical  Words,  Terms  and  Phrases 
to  his  brother  electricians  and  the  public  generally. 

He  trusts  that  this  dictionary  will  be  of  use  to 
electricians,  not  only  by  showing  the  wonderful  extent 
and  richness  of  the  vocabulary  of  the  science,  but  al&o 
by  giving  the  general  consensus  of  opinion  as  to  the  sig- 
nificance of  its  different  words,  terms  or  phrases.  It  is, 
however,  to  the  general  public,  to  whom  it  is  not  only 
a  matter  of  interest  but  also  one  of  necessity  to  fully 
understand  the  exact  meaning  of  electrical  literature, 
that  the  author  believes  the  book  will  be  of  greatest 
value. 

In  order  to  leave  no  doubt  concerning  the  precise 
meaning  of  the  words,  terms  and  phrases  thus  defined, 
the  following  plan  has  been  adopted  of  giving, 

(1)  A  concise  definition  of  the  word,  term  or  phrase. 


(2)  A  brief  statement  of  the  principles  of  the  science 
involved  in  the  definition. 

(3)  "Where  possible  and  advisable,  a  cut  of  the  appar- 
atus  described    or  employed  in  connection  with  the 
word,  term  or  phrase  defined. 

It  will  be  noticed  that  the  second  item  of  the  plan 
makes  the  Dictionary  approach  to  some  extent  the 
nature  of  an  Encyclopedia.  It  differs,  however,  from 
an  encyclopedia  in  its  scope,  as  well  as  in  the  fact  that 
its  definitions  in  all  cases  are  concise. 

Considerable  labor  has  been  expended  in  the  collection 
of  the  vocabulary,  for  which  purpose  electrical  literature 
generally  has  been  explored.  In  the  alphabetical  ar- 
rangement of  the  terms  and  phrases  defined,  much  per- 
plexity has  arisen  as  to  the  proper  catch-word  under 
which  to  place  them.  It  is  believed  that  part  of  the 
difficulty  in  this  respect  has  been  avoided  by  the  free 
use  of  cross-references. 

In  elucidating  the  exact  meaning  of  terms  by  a  brief 
statement  of  the  principles  of  the  science  involved  there- 
in, the  author  has  freely  referred  to  standard  text  books 
on  electricity,  and  to  periodical  literature  generally.  He 
is  especially  indebted  to  works  or  treatises  by  the  fol- 
lowing authors,  viz.:  S.  P.  Thompson,  Larden,  Gum- 
ming, Hering,  Prescott,  Ayrton,  Ayrtonand  Perry,  Pope, 
Lockwood,  Sir  Wm.  Thomson,  Fleming,  Martin  and 
Wetzler,  Preece,  Preece  and  Sivewright,  Forbes,  Max- 
well, De  Watteville,  J.  T.  Sprague,  Culley,  Mascart  and 
Joubert,  Schwendler,  Fontaine,  Noad,  Smee,  Depretz, 
De  la  Eive,  Harris,  Franklin,  Cavallo,  Grove,  Hare, 
Daniell,  Faraday  and  very  many  others. 


IV  PREFACE. 

The  author  offers  his  Dictionary  to  his  fellow  elec- 
tricians as  a  starting  point  only.  He  does  not  doubt 
that  his  book  will  be  found  to  con  tain  many  inaccuracies, 
ambiguous  statements,  and  possibly  doubtful  definitions. 
Pioneer  work  of  this  character  must,  almost  of  neces- 
sity, be  marked  by  incompleteness.  He,  therefore,  in- 
vites the  friendly  criticisms  of  electricians  generally, 
as  to  errors  of  omission  and  commission,  hoping  in 
this  way  to  be  able  finally  to  crystallize  a  complete 
vocabulary  of  eleptrical  words,  terms  and  phrases. 

The  author  desires  in  conclusion  to  acknowledge  his 
indebtedness  to  his  friends,  Mr.  Carl  Hering,  Mr. 
Joseph  Wetzler  and  Mr.  T.  C.  Martin  for  critical  ex- 
amination of  his  proof  sheets  ;  to  Dr.  G.  G.  Faught  for 
examination  of  the  proofs  of  the  parts  relating  to  the 
medical  applications  of  electricity,  and  to  Mr.  C.  E. 
Stump- for  valuable  aid  in  the  illustration  of  the  book  ; 
also  to  Mr.  Geo.  D.  Fowle,  Engineer  of  Signals  of  the 
Pennsylvania  Railroad  Company,  for  information  con- 
cerning their  System  of  Block  Signaling,  and  to  many 
others. 

Central  High  School,  EDWI^  J.  HOUSTON. 

Philadelphia,  Pa. 

September,  18S9. 


A    DICTIONARY 

OF 


Abscissas,  Axis  of One  of  the  axes  of  co-ordi- 
nates used  for  determining  the  position  of  points  in  a  curved 
line. 

Thus  the  position  of  the  point  D,  Fig.  B 
1,  in  the  curved  line  O  D  R,  is  deter- 
mined by  the  vertical  distances  D  1,  and 
D  2,  of  such  point  from  two  straight 
lines  AB,  and  AC,  called  the  axes  of  co- 
ordinates. AC,  is  called  the  axis  of  ab- 
scissas, and  AB,  the  axis  of  ordinates. 
A,  the  point  where  the  lines  ma,y  be 
considered  as  starting  or  originating,  is  ""  pig.  j. 

called  the  point  of  origin.  (See  Co-ordinates,  Axes  of.) 

Absolute.— Complete  in  itself. 

The  terms  absolute  and  relative  are  used  in  electricity  in 
the  same  sense  as  ordinarily. 

Thus,  a  galvanometer  is  said  to  be  calibrated  absolutely 
when  the  exact  current  strengths  required  to  produce  given 
deflections  are  known ;  or,  in  other  words,  when  the  absolute 
current  strengths  are  known  ;  it  is  said  to  bo  calibrated  rela- 
tively when  only  the  relative  current  strengths  required  to 
produce  given  deflections  are  known. 


2  A  DICTIONARY  OF  ELECTRICAL 

The  word  absolute,  as  applied  to  the  units  employed  in  elec- 
trical measurements,  was  introduced  by  Gauss  to  indicate 
the  fact  that  the  values  of  such  units  are  independent  both 
of  the  size  of  the  instrument  employed  and  of  the  value  of 
gravity  at  the  particular  place  where  the  instrument  is  used. 

The  absolute  units  of  length,  mass,  and  time  are  more  prop- 
erly called  the  C.  G.  S.  units,  or  the  centimetre-gramme- 
second  units. 

An  absolute  system  of  units  based  on  the  milligramme, 
millimetre,  and  second,  was  proposed  by  Weber,  and  was 
called  the  millimetre-milligramme-second  units.  It  has  been 
replaced  by  the  C.'G.  S.  units. 

Absolute  Calibration.— (See  Calibration,  Absolute., 

Absolute  Galvanometer. — (See  Galvanometer,  Abso- 
lute.) 

Absolute  Units.— A  term  sometimes  used  to  indicate  the 
C.  G.  S.  units,  but  now  generally  replaced  by  the  term  centi- 
metre-gramme-second units,  or,  more  briefly,  the  C.  G.  S. 
units. 

Absolute  Unit  of  Current.— A  current  of  ten  amperes. 
(See  Ampere.  Units,  Practical.) 

Absolute  Unit  of  Electromotive  Force.— The  one 
hundred  millionth  of  a  volt.  (See  Volt.  Units,  Practical.) 

Absolute  Unit  of  Resistance.— The  one  thousand 
millionth  of  an  ohm.  (See  Ohm.  Units,  Practical.) 

Absolute  Vacuum.— (See  Vacuum,  Absolute). 

Absorption,  Electric The  apparent  soaking  of 

an  electric  charge  into  the  glass  or  other  solid  dielectric  of  a 
Ley  den  Jar  or  Condenser.  (See  Charge.  Condenser.) 

The  capacity  of  a  condenser,  or  its  ability  to  hold  an  elec- 
tric charge,  varies  with  the  time  the  condenser  remains 
charged.  Some  of  the  charge  acts  as  if  it  soaked  into  the 
solid  dielectric,  and  this  is  the  cause  of  the  residual  charge. 
(See  Charge,  Residual.)  Therefore,  when  the  condenser  is 


WORDS,    TERMS   AND   PHRASES. 

discharged,  less  electricity  appears  than  was  passed  in;  hence 
the  term  electric  absorption. 

Absorptive  Power. — The  property  possessed  by  many 
solid  bodies  of  taking1  in  and  condensing  gases  within  their 
pores. 

Carbon  possesses  marked  absorptive  powers.  The  absorp- 
^tion  of  gases  in  tins  manner  by  solid  bodies  is  known  techni- 
cally as  the  occlusion  of  gases.  (See  Occlusion  of  Gases.) 

One  volume  of  charcoal,  at  ordinary  temperatures  and  pres- 
sures, absorbs  of 

A  mmonia 90    volumes 

Hydrochloric  Acid ..85 

Sulphur  Dioxide 65 

Hydrogen  Sulphide 55 

Nitrogen  Monoxide 40 

Carbonic  Acid  Gas 35 

Ethylene. .35 

Carbon  Monoxide 9.42 

Oxygen 9.25 

Nitrogen.. 6.50 

Hydrogen 1.25 

(Saussure.) 
\  <•«'<•  I  r rat  ion. — The  rate  of  change  of  velocity. 

Acceleration  is  thus  distinguished  from  velocity  :  velocity 
expresses  in  time  the  rate-of-change  of  position,  as  a  velocity 
of  three  metres  per  second  ;  acceleration  expresses  in  time 
the  rate-of-change  of  velocity,  as  an  acceleration  of  one  centi- 
metre per  second. 

Since  all  matter  is  inert,  and  cannot  change  its  condition 
of  rest  or  motion  without  the  application  of  some  force,  ac- 
celeration is  necessarily  due  to  some  force  outside  of  matter 
itself.  A  force  may  therefore  be  measured  by  the  accelera- 
tion it  causes  in  a  given  mass  of  matter. 

Acceleration  is  termed  positive  when  the  velocity  is  in- 
creasing, and  negative  when  it  is  decreasing. 

Acceleration,  Unit  of That  acceleration  which 


4  A  DICTIONARY  OP  ELECTRICAL 

will  give  to  a  body  unit-velocity  in  unit-time  ;   as,  for  ex- 
ample, one  centimetre  per  second. 

Bodies  falling  freely  in  a  vacuum,  and  approximately  so  in 
air,  acquire  an  acceleration  which  in  Paris  or  London,  at  the 
end  of  a  second,  amounts  to  about  981  centimetres  per  second, 
or  nearly  32.2  ft.  per  second, 
v 

A  =  — ,  or  in  other  words,  the  acceleration  equals  the  ve- 

T 

locity  divided  by  the  time. 
But,  since  the  velocity  equals  the  Distance,  or  the  Length 

L 
traversed  in  a  unit  of  time,  v  =  — . 

T 


v          T         L 
Therefore,  A  =  —  = =  — ,  or,  the  acceleration  equals  the 

T  T  T2 

1 

length,  or  the  distance  passed  through,  divided  by  the  square 
of  the  time  in  seconds. 

Tiiese  formulae  represent  the  Dimensions  of  Acceleration. 

Accumulator,  or  Condenser.— A  term  often  applied 
to  an  apparatus  called  a  Leyden  Jar  or  Condenser,  which  per- 
mits the  collection  from  an  electric  source  of  a  greater  charge 
than  it  would  otherwise  be  capable  of  giving. 

The  ability  of  the  source  to  give  an  increased  charge  is  due 
to  the  increased  capacity  of  a  plate  or  other  conductor  when 
placed  near  another  plate  or  conductor.  (See  Condenser. 
Jar,  Leyden.) 

Accumulator,  Storage  or  Secondary  Cell.— 
Two  inert  plates  dipping  into  a  liquid  incapable  of  acting 
chemically  on  either  of  them  until  after  the  passage  of  an 
electric  current,  when  they  become  capable  of  furnishing  an 
independent  electric  current. 


WORDS,   TERMS  AND   PHRASES.  5 

This  use  of  the  term  accumulator  is  the  one  most  commonly 
employed.  (See  Storage  Cells  or  Accumulators.) 

Accumulator. —A  term  sometimes  applied  to  Sir  Win. 
Thomson's  Electric  Current  Accumulator. 

The  copper  disc  U,  Fig-.   2,  has    ~p  "     "jT 

freedom  of  rotation,  on  a  horizon- 
tal axis  at  O,  in  a  magnetic  field, 
tin-  lint-sol'  force  of  which,  repre- 
sented by  the  dotted  lines  in  the 
drawing,  pass  down  perpendicu- 
larly into  the  plane  of  the  paper.  fiff-  ~- 

If,  now,  a  current  from  any  source  be  passed  in  the  direc- 
tion A,  O,  B,  C,  A,  through  the  circuit  A,  O,  B,  C,  A,  which 
is  provided  with  spring  contacts  at  O,  and  A,  the  disc  will 
rotate  in  the  direction  of  the  curved  arrow.  This  motion  is 
due  to  the  current  acting-  on  that  part  of  the  disc  which  lies 
between  the  two  contacts — A  and  O.  This  apparatus  is 
known  as  Barlow's  Wheel. 

If,  when  no  current  is  passing-  through  the  circuit,  the  disc 
be  turned  in  the  direction  of  the  arrow,  a  current  is  set  up  in 
such  a  direction  as  would  oppose  the  rotation  of  the  disc. 
(See  Lenz's  Law.) 

If,  however,  the  disc  be  turned  in  the  opposite  direction  to 
that  of  the  arrow,  induction  currents  will  as  before  be  pro- 
duced in  the  circuit.  As  this  rotation  of  the  disc  tends  to 
move  the  circuit  O  A,  towards  the  parallel  but  oppositely 
directed  circuit  B  C,  these  two  circuits,  being-  parallel  and 
in  opposite  directions  tend  to  repel  one  another,  and  there  will 
thus  be  set  up  induced  currents  that  tend  to  oppose  the  motion 
of  rotation,  and  the  current  of  the  circuit  will  therefore  increase 
in  strength.  (Sec  Electro-Dynamics).  Should  then  a  current  be 
started  in  the  circuit,  and  the  original  Held  be  removed,  the 
induction  will  be  continued,  and  a  current  which,  up  to  a  cer- 
tain extent,  increases  or  accumulates,  is  maintained  in  the 
circuit  during  rotation  of  the  disc.  (Larden.) 


6  A  DICTIONARY  OF  ELECTRICAL 

Barlow's  Wheel,  when  used  in  this  manner,  is  known  as 
Thomson's  Electric  Current  Accumulator. 

Accumulator,  Walcr-Oroppiiig An  appa- 
ratus devised  by  Sir  W.  Thomson  for  increasing  the  difference 
of  potential  of  an  electric  charge. 

The  tube  X  Y,   Fig.  3,   connects  with  a 
reservoir  of  water  which  is  maintained  at 
the  zero  potential  of  the  earth.     The  water 
|i  escapes  from  the  openings  at  C  and  D  in 
small  drops  and  falls  on  funnels  provided, 
as    shown,   to  receive  the  separate  drops 
f  A'and  again  discharge  them. 

The  vessels  A,  A',  and  B,  B',  which  are 
Fig.  3.  electrically  connected  as  shown,  are  main- 

tained at  a  certain  small  difference  of  potential,  as  indicated 
by  the  respective  -j-  and  —  signs. 

Under  these  circumstances,  therefore,  C  and  D,  will  be 
charged  inductively  with  charges  opposite  to  those  of  A  and 
B,  or  with  —  and  -j-  electricities  respectively.  As  the  drops 
of  water  fall  on  the  funnels,  the  charges  which  the  funnels 
thus  constantly  receive,  are  given  up  to  B'  and  A',  before 
the  water  escapes.  Since,  therefore,  B,  B',  and  A,  A',  are 
receiving  constant  charges,  the  difference  of  potential  between 
them  must  continually  increase.  This  apparatus  operates 
on  the  same  principle  as  the  replenisher.  The  drops  of  water 
act  as  the  carriers,  and  A,  A',  and  B,  B',  as  the  hollow  vessels. 
(See  Replenisher.) 

Accumulators  or  Condensers ;  Laws  of  Accu- 
mulation of  Electricity.— Sir  W.  Snow  Harris,  by  the 
use  of  his  Unit- Jar,  and  Electric  Thermometer,  deduced  the 
following  laws  for  the  accumulation  of  electricity,  which  we 
quote  from  Noad's  "Student's  Text-Book  of  Electricity."  re- 
vised by  Preece : 

(1)  "Equal  quantities  of  electricity  are  given  off  at  each 
revolution  of  the  plate  of  an  electrical  machine  to  au  un- 


WORDS,    TERMS  AND   PHRASES.  7 

charged  surface,  or  to  a  surface  charged  to  any  degree  of 
saturation." 

(2)  "A  coated  surface  receives  equal  quantities  of  electricity 
in  equal  times ;  and  the  number  of  revolutions  of  the  plate  is 
a  fair  measure  of  the  relative  quantities  of   electricity,   all 
other  things  remaining  the  same." 

(3)  "The  free  action  of  an  electrical  accumulation  is  esti- 
mated by  the  interval  it  can  break  through,  and  is  directly 
proportional  to  the  quantity  of  electricity." 

(4)  "The  free  action  is  inversely  proportional  to  the  sur- 
face." 

(5)  "  When  the  electricity  and  the  surface  are  increased  in 
the  same  ratio,  the  discharging  interval  remains  the  same ; 
but  if,  as  the  electricity  is  increased,  the  surface  is  diminished, 
the  discharging  interval  is  directly  as  the  square  of  the  quan- 
tity of  electricity." 

(6)  "The  resistance  of  air  to  discharge  is  as  the  square  of 
the  density  directly." 

According  to  some  later  investigations,  the  quantity  a 
plane  surface  can  receive  under  a  given  density  depends  on 
the  linear  boundary  of  the  surface  as  well  as  on  the  area  of 
the  surface. 

"The  amount  of  electrical  charge  depends  on  surface  and 
linear  extension  conjointly.  There  exists  in  every  plane 
surface  what  may  be  termed  an  electrical  boundary,  having 
an  important  relation  to  the  grouping  or  disposition  of  the 
electric  particles  in  regard  to  each  other  and  to  surrounding 
matter.  This  boundary  in  circles  or  globes  is  represented  by 
their  circumferences.  In  plane  rectangular  surfaces,  it  is  by 
their  linear  extension  or  perimeter.  If  this  boundary  be  con- 
stant, their  electrical  charge  varies  with  the  square  root  of 
the  surface.  If  the  surface  be  constant  the  charge  varies  with 
the  square  root  of  the  boundary.  If  the  surface  and  boun- 
dary both  vary,  the  charge  varies  with  the  square  root  of  the 
surface  multiplied  into  the  square  root  of  the  boundary." 


8  A  DICTIONARY  OF  ELECTRICAL 

These  laws  apply  especially  to  continuous  surfaces  taken  as 
a  whole,  and  not  to  surfaces  divided  into  separate  parts. 

By  electrical  charge  Harris  meant  the  quantity  sustained 
on  a  given  surface  under  a  given  electrometer  indication  ;  by 
electrical  intensity,   he  meant  the  indication  of  the  electro- 
meter corresponding-  to  a  given  quantity  on  a  given  surface. 
For  further  information  see  Condensers,  Capacity  of. 
A.  C.  C. — An  abbreviation  used  in  medical  electricity  for 
Anodic  Closure  Contraction,  or  the  contraction  observed  on 
closing  the  circuit  when  the  anode  is  lying  over  the  muscle. 

The  term  anode  is  sometimes,  as  above,  used  to  indicate  the 
positive  terminal  of  an  electric  battery  or  source.   (See  Anode.) 
Achromatic. — Free  from  false  coloration. 
Images  formed  by  ordinary  lenses  do  not  possess  the  true 
colors  of  the  object,  unless  the  edges  of  the  lenses  are  cut  off 
by  the  use  of  a  diaphragm;  i.  e.,  an  opaque  plate  with  a  circu- 
lar central  opening.     The  edges  of  the  lenses  disperse  the  light 
like   an    ordinary  prism,   and    so    produce    rainbow-colored 
(prismatic)  fringes  in  the  image.     The  use  of  an  achromatic 
lens  is  to  obviate  this  false  coloration. 

The  ray  of  light  entering  the  prism  ABC,  Fig.  4, 
suffers  dispersion  (separation  into  prismatic  colors).  This 
dispersion  in  the  same  medium  is  proportional  to  the  angle  g, 
between  the  incident  and  emergent  faces,  called  the  refract- 
ing angle. 

If,  now,  another  prism  BCD,  of 
the  same  material,  whose  refract- 
'"^'  an^'le  .'/'-  is  <'q»a1  to  g,  is  <-om- 
"R>  bined  with  the  first  prism  in  the 
manner  shown  in  Fig.  4,  it  will 
produce  an  equal  but  opposite  dis- 
persion, so  that  the  ray  of  light 
will  emerge  at  R,  free  from  rain- 
bow tints,  but  parallel  to  its  origi- 
nal direction. 


WORDS,   TERMS   AND  PHRASES. 


The  variety  of  glass  called  crown  glass  produces  only  half 
s  great  dispersion  of  light  as  the  variety  called  flint  glass, 


If  the  prism  ABC, 
B  D 


under  the  same  refracting  angle  g. 
of  crown  glass,  Fig.  5,  whose 
angle  g,  is  twice  as  great  as  the 
refracting  angle  g',  of  the  prism 
BCD,  of  Hint  glass,  be  con- 
nected with  it  in  the  manner 
shown,  then  the  ray  E,  will  be 
transmitted  free  from  color,  but 
if  ill  not  emerge  parallel  to  its 
original  direction  ;  in  other 
words,  it  suffers  refraction  or  bending.  (See  Refraction.) 

The    construction  of    achromatic  lenses  is  based  on  this 
principle. 


Fig.  C. 

The  crown  glass  is  generally  made  with  two  convex  sur- 
faces ;  the  flint  glass,  with  one  concave  and  one  plane  sur- 
face, as  shown  in  Fig.  6. 

Sometimes  both  surfaces  of  the  flint  glass  are  made  curved, 
as  in  Fig.  7. 


Fig.  7. 

Aclinic  Line. — The  magnetic  equator,  or  a  line  on  the 
earth's  surface  connecting  places  where  the  magnetic  needle 
has  no  inclination  or  dip. 

The  magnetic  equator  is  not  a,  circle,     It  cuts  the  geograph- 


10  A   DICTIONARY   OF   ELECTRICAL 

ical  equator  at  2°  E.  long.,  and  at  170°  W.  long.  (See  Inclina- 
tion Map  or  Chart.) 

Acoustic  Engraving.— (See  Engraving,  Acoustic.) 

Acoustic  Telegraph. — A  non-recording  system  of  tele- 
graphic communication,  in  which  the  dots  and  dashes  of  the 
Morse  system,  or  the  deflections  of  the  needle  in  the  needle 
system,  are  replaced  by  sounds  that  follow  one  another  at  in- 
tervals that  represent  the  dots  and  dashes,  or  the  deflections 
of  the  needle,  and  thereby  the  letters  of  the  alphabet. 

Steinheil  and  Bright  each  invented  acoustic  systems  of  teleg- 
raphy in  which  electro-magnetic  bells  are  used.  Morse  in- 
vented a  Sounder,  for  this  purpose,  which  is  used  very 
generally.  (See  Sounder,  Telegraphic.) 

For  details  of  the  apparatus  and  system  see  Telegraphy, 
American  or  Morse  system  of. 

Actinic  Photometer.— (See  Photometer,  Actinic.) 

Actinic  Rays. — The  rays  of  light,  or  other  forms  of  radi- 
ant energy  that  possess  the  power  of  effecting  chemical  de- 
composition. (See  Decomposition.) 

All  rays  of  light,  and  even  some  of  those  invisible  to  the 
human  eye,  are  actinic  to  some  particular  chemical  substance 
or  another.  Whether  the  ether  waves  produce  the  effects  of 
heat,  light,  or  chemical  decomposition  depends  on  the  nature 
of  the  material  on  which  they  fall,  as  well  as  on  the  character 
of  the  waves  themselves. 

Actinism. — The  chemical  effects  of  light,  as  manifested  in 
the  decomposition  of  various  substances. 

Under  the  influence  of  the  sun's  light,  the  carbonic  acid  ab- 
sorbed by  the  leaves  of  plants  is  decomposed  in  the  living  leaf 
into  carbon,  which  is  retained  by  the  plant  for  the  formation 
of  its  woody  fibre  or  ligneous  tissue,  and  oxygen,  which  is 
thrown  off. 

The  bleaching  of  curtains,  carpets,  and  other  fabrics  ex- 
posed to  sunlight  is  caused  by  the  actinic  power  of  the  light. 
The  photographic  picture  is  impressed  by  the  actinic  power  of 


WORDS,    TERMS  AND   PHRASES.  11 

light  on  a  plate  covered  with  some  sensitive  metallic  salt, 
generally  silver. 

Action,  Local An  irregular  dissolving  or  con- 
sumption of  the  zinc  or  positive  element  of  a  voltaic  battery, 
by  the  fluid  er  electrolyte,  when  the  circuit  is  open  or  broken, 
as  well  as  when  closed,  or  in  regular  action. 

Local  action  is  due  to  impurities,  such  as  carbon,  iron,  ar- 
senic, etc.,  in  the  positive  plate.  These  impurities  form  with 
the  positive  element  little  voltaic  couples,  and  thus  direct  the 
corrosive  action  of  the  liquid  to  portions  of  the  plate  near  the 
impurities.  Local  action  causes  a  waste  of  energy.  It  may 
be  avoided  by  amalgamation  of  the  zinc.  (See  Zinc,  Amal- 
gamation of.) 

Action,  Local A  term  proposed,  but  not  gener- 
ally adopted,  to  indicate  the  wasteful  currents  in  the  pole 
pieces  or  cores  of  dynamo-electric  machines. 

These  currents  are  now  generally  known  as  Eddy,  Foucault, 
or  Parasitical  Currents.  (See  Currents,  Eddy,  Foucault, 
Local,  or  Parasitical.) 

Action,  Ulagiic-Crj  stallic — (See  Magne- Crystal- 
lie  Action.) 

Action,  Unit  of —  — A  rate  of  working,  which  will 
perform  one  unit  of  work  per  second. 

In  C.  G.  S.  units,  the  activity  of  one  erg  per  second.  This 
unit  is  very  small.  One  Watt,  the  practical  unit  of  power,  is 
equal  to  ten  million  ergs  per  second.  (See  Watt.) 

The  unit  of  activity  generally  used  for  mechanical  power  is 
one  horse-power,  or  746  watts.  (See  Horse-power.) 

Activity. — The  work  done  per  second  by  any  agent. 

W orh-per-second,  or,  as  generally  termed  in  the  United 
States,  Power,  or  Rate  of  Doing  Work.  (See  Power.) 

A.  D.  C. — An  abbreviation  used  in  medical  electricity  for 
Anodic  Duration  Contraction. 

Adhesion. — The  attraction  that  exists  between  unlike 
molecules.  (See  Attraction,  Molecular.) 


12  A  DICTIONARY  OF  ELECTRICAL 

Adiallierniancy.— Opacity  to  heat. 

A  substance  is  said  to  be  diathermanous  when  it  is  trans- 
parent to  heat.  Clear,  colorless  crystals  of  rock  salt  are  very 
transparent  both  to  light  and  to  heat.  Rock  salt,  covered  with 
a  layer  or  deposit  of  lamp-black  or  soot,  is  quite  transparent 
to  heat.  An  adiathermanous  body  is  one  which  is  opaque 
to  heat. 

Heat  transparency  varies  not  only  with  different  sub- 
stances, but  also  with  the  nature  of  the  source  from  which 
the  heat  is  derived.  Thus,  a  substance  may  be  opaque  to  the 
heat  from  a  non-luminous  source,  such  as  a  vessel  filled  with 
boiling1  water,  while  it  is  comparatively  transparent  to  that 
from  a  luminous  source,  such  as  an  incandescent  solid,  or  the 
voltaic  arc. 

A  similar  difference  exists  as  regards  transparency  to 
light.  A  colorless  glass  will  allow  light  of  any  color  to  pass 
through  it.  A  blue  glass  will  allow  blue  light  to  pass 
freely  through  it,  but  will  completely  prevent  the  passage 
of  any  red  light ;  and  so  with  other  colors. 

/Epinus'  Condenser. — (See  Condenser.) 

Affinity,  Chemical Atomic  attractions. 

The  force  that  causes  atoms  to  unite  and  form  chemical 
molecules. 

Atomic,  or  chemical  attraction  generally  results  in  a 
loss  of  the  characteristic  qualities,  or  properties,  that  dis- 
tinguish one  kind  of  matter  from  another.  In  this  respect 
it  differs  from  adhesion,  or  the  force  which  holds  unlike 
molecules  together.  (See  Adhesion.)  If,  for  example,- sulphur 
is  mixed  with  lamp-black,  no  matter  how  intimate  the  mix- 
ture, the  separate  particles,  when  examined  by  a  glass,  ex- 
hibit their  peculiar  color,  lustre,  etc.  If,  howerer,  the  sul- 
phur is  chemically  united  with  the  carbon,  a  colorless,  trans- 
parent, mobile  liquid,  called  carbon  bisulphide,  results,  that 
possesses  a  disagreeable,  penetrating  odor. 

Chemical  affinity,  or  atomic  combination,  is  influenced  by 
a  variety  of  causes,  viz, ; 


WORDS,    TERMS  AND  PHRASES.  13 

(1)  Cohesion.      Cohesion,  by  binding  the  molecules  more 
firmly  together,  opposes  their  mutual  atomic  attractions. 

A  solid  rod  of  iron  will  not  readily  burn  in  the  flame  of  an 
ordinary  lamp,  but  if  the  cohesion  be  overcome  by  reducing 
the  iron  rod  to  filings,  it  burns  with  brilliant  scintillations 
when  dropped  into  the  same  flame. 

(2)  Solution.     Solution,    by    imparting    to    the    molecules 
greater    freedom    of    motion,    favors    their    chemical    com- 
bination. 

(3)  Heat.    Heat  favors  atomic  combination  by  decreasing 
the  cohesion,  and  possibly,   by  altering  the  electrical  rela- 
tions of  the  atoms.     If  too  great,  heat  may  produce  decom- 
position.    (See  Dissociation.) 

(4)  Light.      Decomposition,   or  the  lessening  of  chemical 
affinity  through  the  agency  of  light,  is  called  Actinism.  Light 
also  causes  the  direct  combination  of  substances.     A  mix- 
ture of  equal   volumes  of  hydrogen  and  chlorine  vinites  ex- 
plosively when  exposed  to  the  action  of  full  sunlight.     (See 
Actinism.) 

(5)  Electricity.     An  electric  spark  will  cause  an  explosive 
combination  of  a  mixture  of  oxygen  and  hydrogen.     Electric- 
ity also  produces  chemical  decomposition.     (See  Electrolysis.) 

Agoiie. — A  line  connecting  places  on  the  earth's  surface 
where  the  magnetic  needle  points  to  the  true  geographical 
north. 

The  line  of  no  declination  or  variation  of  a  magnetic  needle. 
(See  Declination  or  Variation  of  Magnetic  Needle.) 

As  all  the  places  on  the  earth  where  the  magnetic  needle 
points  to  the  true  north  may  be  arranged  on  a  few  lines,  it 
will  be  understood  that  the  pointing  of  the  magnetic  needle 
to  the  true  geographical  north  is  the  exception  and  not  the 
rule.  In  many  places,  however,  the  deviation  from  the  true 
geographical  north  is  so  small  that  th£  direction  of  the  needle 
may  be  regarded  as  approximately  due  north. 

Agonic.— Pertaining  to  the  Agone. 


14 


A  DICTIONARY  OF  ELECTRICAL 


Air-Bla§t.— An  invention  of  Prof.  Elihu  Thomson  to  pre- 
vent the  injurious  action  of  destructive  sparking  at  the  com- 
mutator of  a  dynamo-electric  machine. 

A  thin,  forcible  blast  of  air  is  delivered  through  suitable 
tubes  at  points  on  the  three-part  commutator  cylinder  of  the 
Thomson  Houston    dynamo,    where    the  collecting    brushes 
bear  on  its  surface.     The  effect  is 
to  blow  out  the  arc  and  thus  pre- 
vent its  destructive  action  on  the 
commutator  segments.     The  use  of 
the  air-blast  also  permits  the  free 
application  of  oil.  thus  further  avoid- 
ing wear. 

The  blast-nozzles  are  shown  at 
Bs,  Bs,  Fig.  8,  near  the  collecting 
brushes. 

The  air-supply  is  ob- 
tained from  a  centri- 
fugal blower  attached 
directly  to  the  shaft  of 
the  machine.  Its  con- 
struction and  operation 
will  be  readily  under-  ^ 
stood  from  an  inspec- 
tion of  Fig.  9,  in  which 
the  top  is  removed  for 
a  ready  examination  of 
the  interior  parts. 


Mill-ill*.  Electric Various  automatic  devices  by 

which  attention  is  called  to  the  occurrence  of  certain  events, 
such  as  the  opening  of  a  door  or  window;  the  stepping  of  a 
person  on  a  mat  or  staircase ;  the  rise  or  fall  of  temperature 
beyond  a  given  predetermined  point ;  or  to  ca-ll  a  person  to  a 
telegraphic  or  telephonic  instrument. 


WORDS,  TERMS  AND  PHRASES. 


15 


Electric  alarms  are  operated  by  either  the  closing  or  the 
opening  of  nn  electric  circuit,  generally  the  former,  by  means 
of  which  an  electro-magnetic  or  mechanical  bell  is  rung. 

Electric  alarms  may  be  di- 
vided into  two  classes,  viz.  : 

1.  Mechanically     operated 
alarms,  or  those  operated  by 
clock-work,  that  is  started  by 
means  of  an  electric  current. 

2.  Those  in  which  the  alarm 
is  both  set  into  operation  and 
operated  by  the  action  of  an 
electric  current. 

In  Fig.  10,  is  shown  the 
general  construction  of  an 
electrically  started  mechani- 
cal alarm.  The  attraction  of 
the  armature  B,  by  the  electro- 
magnet A,  moves  the  arma- 
ture lever  pivoted  at  C,  and 
thus  i-eleases  the  catch  e,  and 
permits  the  spring  or  weight  Fi9-  10. 

connected  with  the  clock  movement  to  set  it  in  motion  and 
strike  the  bell. 

Electrically  actuated  alarm-bells  are  generally  of  the 
automatic  make-and-break  form.  The  striking  lever  is 
operated  by  the  attraction  of  the  armature  of  an  electro- 
magnet, and  is  provided  with  a  contact-point,  so  placed  that 
when  the  hammer  is  drawn  away  from  the  bell,  on  the 
electro-magnet  losing  its  magnetism,  the  contact-point  is 
closed,  but  when  it  is  drawn  towards  the  bell  the  contact  is 
opened.  When,  therefore,  the  hammer  strikes  the  bell, 
the  circuit  is  opened,  and  the  electro-magnet  releases  its 
armature,  permitting  a  spring  to  again  close  the  contact  by 
moving  the  striking  lever  away  from  the  bell.  Once  set  into 


10 


A  DICTIONARY  OF  ELECTRICAL 


action,  these  movements  arc  repeated  while  there  is  battery 
power  sufficient  to  energize  the  magnet 

la  Fig-.  11,  the 
bal  lory  terminals 
are  connected 
with  the  right  and 
lefthandbinding- 
posts,  P  and  M. 
The/iammerK,is 
connected  with  a 
striking  lever, 
which  forms  part 
of  the  circuit,  and 
which  is  attached 
to  the  amnature 
o  f  the  electro- 
magnet  e.  A  me- 
tallic spring  g,  bears  against  the  armature  when  the  latter 
is  away  from  the  magnet,  but  does  not  touch  the  armature 
when  it  is  moved  towards  the  magnet.  The  movements  of 
the  armature  thus  automatically  open  and  close  the  circuit 
of  the  electro-magnet. 

This  form  of  make-and-break  is  called  an  automatic  make- 
and-break. 

Alarms,  Electric  Burglar An  electric  device 

to  automatically  announce  the  opening-  of  a  door,  window, 
closet,  drawer,  or  safe,  or  the  passage  of  a  person  through 
a  hallway,  or  on  a  stairway. 

Electric  burglar  alarm  devices  generally  consist  in  mechan- 
ism for  the  operation  of  an  automatic  make-and-break  bell 
on  the  closing  of  an  electric  circuit.  The  bell  may  either 
continue  ringing  only  while  the  contact  remains  closed,  or, 
may,  by  the  throwing  on  of  a  local  circuit  or  battery,  con- 
tinue ringing  until  stopped  by  some  non-automatic  device, 
such  as  a  hand-switch. 


WORDS,   TERMS  JtND  PHRASES.  17 

The  alarm-bell  is  stationed  either  in  the  house  when  occu- 
pied, or  on  the  outside  when  the  house  is  temporarily  vacated, 
or  may  connect  directly  witli  the  nearest  police  station. 

Burglar-alarm  apparatus  is  of  a  variety  i 
of  forms.  Generally,  devices  are  provided 
by  means  of  which,  in  case  of  house  pro- 
tection, an  annunciator  shows  the  exact 
part  where  an  entrance  has  been  at- 
tempted. (See  Annunciator.)  Switches 
are  provided  for  disconnecting-  all  or  parts 
of  the  house  from  the  alarm  when  so  de- 
sired, as  well  as  to  permit  windows  to  be 
partly  raised  for  purposes  of  ventilation 
without  sounding  the  alarm.  A  clock  is  ^ 

frequently  connected  with  the  alarm  for 
the  purpose  of  automatically  disconnecting  any  portion  of 
the  house  at  or  for  certain  intervals  of  time. 

Fig.  12,  shows  a  burglar  alarm  with  annunciator,  switches, 
switch-key,  cut-off,  and  clock. 

Alarm§,   Electric   Burglar Yale   Lock 

Switch  for. — An  alarm  whereby  the  opening  of  a  door  by 
an  authorized  party  provided  with  the  regular  key  will  not 
sound  an  alarm,  but  any  other  opening  will  sound  such  alarm. 
\  I;  .  .MS.  Electric  Fire  or  Temperature —In- 
struments for  automatically  sounding  an  alarm  on  an  increase 
of  temperature  beyond  a  certain  predetermined  point. 

Fire-alarms  are  operated  by  thermostats,  or  by  means  of 
mercurial  contacts;  i.  e.,  a  contact  closed  by  the  expansion  of  a 
column  of  mercury.  (See  Thermostat.) 

In  systems  of  fire-alarm  telegraphs,  the  alarm  is  automati- 
<  ally  sounded  in  a  central  police  station  and  in  the  district 
fire-engine  house.  (See  Telegraphy,  Fire-alarm.) 

The  action  of  mercurial  contacts  is  dependent  on  the  fact 
that,  as  the  mercury  expands  by  the  action  of  the  heat,  it 
reaches  a  contact-point  placed  in  the  tube  and  thus  completes 


18  A  DICTIONARY   OF  ELECTRICAL 

the  circuit  through  its  own  mass,  which  forms  the  other  or 
movable  contact.  Sometimes  both  contacts  are  placed  on 
opposite  sides  of  a  tube  and  are  closed  when  the  mercury 
i-eaches  them. 

Mercurial-temperature  or  thermostat  alarms  are  employed 
in  hot-houses,  incubators,  tanks,  and  buildings,  for  the 
purpose  of  maintaining  a  uniform  temperature. 

Alarms,  Electric  Water  or  Liquid  Level 

Devices  for  sounding  an  alarm  electi'ically  when  a  water  sur- 
face varies  materially  from  a  given  level. 

An  electric  bell  is  placed  in  a  circuit  that  is  automatically 
closed  or  broken  by  the  movement  of  contact-points  operated 
by  a  change  of  liquid  level. 

Alarms,  Telegraphic Alarm  bells  for  calling 

the  attention  of  an  operator  to  a  telegraphic  instrument  when 
the  latter  is  of  the  non-acoustic  or  needle  type. 

In  acoustic  systems  of  telegraphy,  the  sounds  themselves 
are  generally  sufficient  for  this  purpose. 

Alarms,  Telephonic An  alarm-bell  for  calling 

a  correspondent  to  the  telephone. 

These  alarms  generally  consist  of  magneto-electric  bells. 
(See  Magneto-Electric  Call-Bell) 

Alcohol,  Electrical  Rectification  of. A 

process  whereby  the  bad  taste  and  odor  of  alcohol,  due  to  the 
presence  of  aldehydes,  are  removed  by  the  electrical  con- 
version of  the  aldehydes  into  true  alcohols  through  the  ad- 
dition of  hydrogen  atoms. 

An  electric  current  sent  through  the  liquid,  between  zinc 
electrodes,  liberates  oxygen  and  hydrogen  from  the  decom- 
position of  the  water.  The  hydrogen  converts  the  aldehydes 
into  alcohol,  and  deprives  the  products  of  their  fusel  oil, 
while  the  oxygen  forms  insoluble  zinc  oxide. 

Algebraic  Notation. — (See  Notation,  Algebraic.) 

Alphabet,  Telegraphic An  arbitrary  code 

consisting  of  dots  and  dashes,  sounds,  deflections  of  a  mag- 


WORDS,   TERMS   AND  PHRASES.  19 

netic  needle,  flashes  of  light,  or  movements  of  levei-s,  follow- 
ing one  another  in  a  given  predetermined  order,  to  represent 
the  letters  of  the  alphabet  and  the  numerals. 
Alphabet,    Morse's  Telegraphic 

Various  groupings  of  dots  and  dashes,  or  deflections  of  a 
magnetic  needle  to  the  right  and  left,  that  represent  the  letters 
of  the  alphabet  or  other  signs. 

In  the  Morse  alphabet  dots  and   dashes  are  employed  in 
recording  systems,  and  sounds  of  varying  lengths,  correspond- 
ing to  the  dots  and  dashes  in  the  sounder  system. 
AMERICAN  MORSE  CODE. 
ALPHABET. 

a    —  n 

b    -  o    - 

c     --    -  p    - 

d    -  q    - 

e     -  r    -    -  - 

f     -  B    - 

g t     - 

h    u 

i      . .  v 

k x 

i  y  - 

m 


NUMERALS. 
1      -  — 
2 


5 0     

PUNCTUATION    MARKS. 

Period    -  Interrogation    — 

Comma Exclamation 


20  A  DICTIONARY  OP  ELECTRICAL 

In  the  needle  telegraph,  the  code  is  similar  to  that  used  in 
the  Morse  Alphabet.     (See  Telegraphy,  Single-needle.) 

Alphabet,    Telegraphic:    Continental  Code. 


Single 

Single 

Printing 

Needle 

Printing 

Needle 

a    .  

xX 

n   . 

/\ 

b    

XXXN 

o    

/// 

C     .  . 

.XxXx 

p   .  .  . 

^//^ 

d    

Xxx 

q    

//-./ 

e    . 

X 

r    .  . 

xXs 

f    

xxXs 

s    ... 

\\\ 

g   

//    N 

t    

/ 

h    .... 

\xxx 

u    ..  — 

xxX 

i     .. 

XX 

v    ...  

\N\X 

j     

^/// 

w  .  

^// 

k   

/^/. 

X     ..  

/xxX 

1     .  —  .  . 

xXss 

y   

/^'// 

m  * 

// 

z    

//  \\ 

Similar  symbols  are  employed  for  the  numerals  and  the 
punctuation  marks. 

It  will  be  observed  that  it  is  mainly  in  the  characters  of  the 
American  Morse,  in  which  spaces  are  used,  that  the  Conti- 
nental characters  differ  from  the  American.  This  is  due  to 
the  use  of  the  needle  instrument.  A  movement  or  deflection 
of  the  needle  to  the  left  signifies  a  dot;  a  movement  to  the 
right,  a  dash. 

For  methods  of  receiving  the  alphabet,  see  Sounder,  Morse 


WORDS,   TERMS  AND  PHRASES.  21 

Telegraphic.  Recorder,  Morse's.  Recorder,  Chemical.  Re- 
corder, Siphon.  Relay  or  Receiving  Magnet. 

All-night  Arc  Lamp.— (See  Double- Carbon  Arc  Lamp.) 

Alloy. — A  combination,  or  mixture,  of  two  or  more  metallic 
substances. 

Alloys  in  most  cases  appear  to  be  true  chemical  compounds. 
In  a  few  instances,  however,  they  may  form  simple  mixtures. 

The  composition  of  a  few  important  alloys  is  here  given  : 

Solder,  plumber's  ;  Tin  60  parts,  Lead  34  parts. 

Pewter,  hard  ;  Tin  93  parts,  Lead  8  parts. 

Britannia  metal ;  Tin  100  parts,  Antimony  8  parts,  Copper  4 
parts,  Bismuth  1  part. 

German  silver  ;  Copper  50,  Zinc  25,  Nickel  25  parts. 

Type  metal  ;  Lead  80,  Antimony  30  parts. 

Brass,  white  ;  Copper  65,  Zinc  35  parts. 

Brass,  red  ;  Copper  90,  Zinc  10  parts. 

Speculum  metal ;  Copper  67,  Tin  33  parts. 

Bell  metal ;  Copper  78,  Tin  22  parts. 

Aluminium  bronze ;  Copper  90,  Aluminium  10  parts. 

Alloys,  Palladium (See  Palladium  Alloys.) 

Allotropy,  Allotropie  Stale.— A  modification  of  a 
substance,  in  which,  without  changing  its  chemical  compo- 
sition, it  assumes  a  condition  in  which  its  physical  and  chem- 
ical properties  are  distinct  from  those  it  ordinarily  possesses. 

Thus  the  element  carbon  occurs  in  three  widely  different 
allotropic  states,  viz.: 

(1)  As  charcoal,  or  ordinary  carbon  ; 

(2)  As  graphite,  or  plumbago  ;  and 

(3)  As  the  diamond, 

Alternating  Current.— An  electric  current  that  alter- 
nately flows  in  opposite  directions.  (See  Current,  Alterna- 
ting.) 

Alternating  Motor.— (See  Motor,  Alternating  Cur- 
rent.) 


22  A  DICTIONARY  OF  ELECTRICAL 

Alternating  Dynamo-Electric  Machine.— A  <ty- 
namo-electric  machine  that  furnishes  alternating  currents, 
(See  Dynamo-Electric  Machine.) 

Alternating  System  of  Distribution.— A  system  of 
electric  distribution  in  which  lamps,  motors,  or  other  electro- 
receptive  devices  are  operated  by  means  of  alternating  cur- 
rents that  are  sent  over  the  line,  but  which,  before  passing 
through  said  devices,  are  modified  by  apparatus  called  con- 
verters or  transformers.  (See  Converter  or  Transformer.) 

For  details  of  the  alternating  system  of  distribution,  see 
Systems  of  Distribution  by  Alternating  Currents. 

Alternatives,  Voltaic A  term  used  in  medical 

electricity  to  indicate  sudden  reversals  of  polarity  of  the  elec- 
trodes of  a  voltaic  battery. 

An  alternating  current  from  a  voltaic  battery,  obtained  by 
the  use  of  a  suitable  commutator. 

Sudden  reversals  of  pol  irity  produce  more  energetic  effects 
of  muscular  contraction  than  do  simple  closures  or  comple- 
tions of  the  circuit. 

Since  all  electricity  is  one  and  the  same  thing  or  force,  what- 
ever its  source,  the  necessity  for  the  term  voltaic  alternative 
in  place  of  alternating  current  is  by  no  means  clear.  The 
only  consideration  that  would  appear  to  warrant  its  con- 
tinued use  is  that  the  alternating  currents  obtained  from 
the  voltaic  batteries  generally  employed  in  electro  thera- 
peutics, by  the  action  of  a  pole-changer,  possess  a  much 
smaller  electro-motive  force  than  do  faradic  currents,  which 
are  also  alternating. 

Amalgam. — The  combination  or  mixture  of  a  metal  with 
mercury. 

Amalgam,  Elcctrie A  substance  with  which 

the  rubbers  of  the  ordinary  frictional  electric  machines  are 
covered. 

Electric  amalgams  are  of  various  compositions.  The  fol- 
lowing is  excellent  : 


WORDS,   TERMS  AND  PHRASES.  23 

Melt  together  five  parts  of  zinc  and  three  of  tin,  and  gradu- 
ally pour  the  molten  metal  into  nine  parts  of  mercury. 
Shake  the  mixture  until  cold,  and  reduce  to  a  powder  in 
a  warm  mortar.  Apply  to  the  cushion  by  means  of  a  thin 
layer  of  stiff  grease. 

Mosaic  gold,  or  bisulphide  of  tin,  and  powdered  graphite, 
both  act  as  good  electric  amalgams. 

An  electric  amalgam  not  only  acts  as  a  conductor  to  carry 
off  the  negative  electricity,  but  being  highly  negative  to  the 
glass,  produces  a  far  higher  electrification  than  would  leather 
or  chamois. 

Amalgamation.— The  act  of  forming  an  amalgam,  or 
effecting  the  combination  of  a  metal  with  mercury. 

Amalgamation  of  Zinc  Battery  Plates. — Cover- 
ing the  surface  of  the  zinc  plate  of  a  voltaic  cell  with  a  thin 
layer  of  amalgam  in  order  to  avoid  local  action.  (See  Action, 
Local.) 

For  details  of  process,  see  Zinc,  Amalgamation  of. 

Amber. — A  resinous  substance,  generally  of  a  transparent, 
yellow  color. 

Amber  is  interesting  electrically  as  being  believed  to  be  the 
substance  in  which  the  properties  of  electric  attractions  and 
repulsions  imparted  by  friction  or  rubbing  were  first  noticed. 
It  was  called  by  the  Greeks  rj \mrpov  from  which  the  word 
electricity  is  derived.  This  property  was  mentioned  by  the 
Greek,  Thales  of  Miletus,  600  B.  c.,  as  well  as  by  Theophrastus. 

Amorphous.— Having  no  definite  crystalline  form. 

Mineral  substances  have  certain  crystalline  forms,  that 
are  as  characteristic  of  them  as  are  the  forms  of  animals  or 
plants.  Under  certain  circumstances,  however,  they  occur 
without  definite  crystalline  form,  and  are  then  said  to  be  amor- 
phous solids. 
Ampere.— The  practical  unit  of  electric  current. 

Such  a  current  (or  rate  of  flow  or  transmission  of  electricity) 


24  A  DICTIONARY  OF  ELECTRICAL 

as  would  pass  with  an  E.  M.  F.  of  one  volt  through  a  circuit 
whose  resistance  is  equal  to  one  ohm.  That  is  to  say,  a  cur- 
rent of  the  definite  strength  that  would  How  through  a  circuit 
of  a  certain  resistance  and  with  a  certain  electro-motive 
force.  (See  Electro-Motive  Force.  Volt.  Resistance.  Ohm.) 

Since  the  ohm  is  the  practical  unit  of  resistance,  and  the  volt 
the  practical  unit  of  electro-motive  force,  the  ampere,  or  the 
practical  vinit  of  current,  is  the  current  that  would  flow  against 
unit  resistance,  under  unit  pressure  or  electro-motive  force. 

To  make  this  clearer,  take  the  analogy  of  water  flowing 
through  a  pipe  under  the  pressure  of  a  column  of  water.  That 
which  causes  the  fl'dw  is  the  pressure  or  head  ;  that  which 
resists  the  flow  is  the  friction  of  the  pipe,  which  will  vary 
with  a  number  of  circumstances.  The  rate  of  flow  may  he 
represented  hy  so  many  cubic  inches  of  water  per  second. 

As  the  pressure  or  head  increases,  the  flow  increases  pro- 
portionally ;  as  the  resistance  increases,  the  flow  diminishes. 

Electrically,  electro-motive  force  corresponds  to  the  pres- 
sure or  head  of  the  water,  and  resistance  to  the  friction  of  the 
water  and  the  pipe.  The  ampere,  which  is  the  unit  rate  of 
flow  per  second,  may  therefore  be  represented  as  follows, 

E 

viz.:    c  =  — ,   as  was  announced  by  Ohm  in  his  law.     (See 
R 

Ohm's  Law.) 

This  expression  signifies  that  C,  the  current  in  amperes,  is 
equal  to  E,  the  electro-motive  force  in  volts,  divided  by  B,  the 
resistance  in  ohms. 

We  measure  the  rate  of  flow  of  liquids  as  so  many  cubic 
inches  or  cubic  feet  per  second — that  is,  in  units  of  quantity. 
We  measure  the  rate  of  flow  of  electricity  as  so  much  elec- 
tricity per  second.  The  electrical  unit  of  quantity  is  called  the 
Coulomb.  (See  Coulomb.)  The  coulomb  is  such  a  quantity 
as  would  pass  in  one  second  through  a  circuit  in  which  the 
rate  of  flow  is  one  ampere. 


WORDS,   TERMS  AND   PHRASES.  35 

An  ampere  per  second  is  therefore  equal  to  one  coulomb. 

The  electro-magnetic  unit  of  current  is  such  a  current  that, 
passed  through  a  conducting  wire  bent  into  a  circle  of  the 
radius  of  one  centimetre,  would  attract  a  unit  magnetic  pole 
held  at  its  centre,  and  sufficiently  long  to  practically  remove 
the  other  pole  from  the  influence,  with  unit  force,  i.e.,  the 
•force  of  one  dyne.  (See  Dyne.)  The  ampere,  or  practical 
electro-magnetic  unit,  is  one-tenth  of  such  a  current ;  or,  in 
other  words,  the  absolute  unit  of  current  is  ten  amperes. 

An  ampere  may  also  be  defined  by  the  chemical  decom- 
position the  current  can  effect  as  measured  by  the  quantity 
of  hydrogen  liberated,  or  metal  deposited. 

Defined  in  this  way,  an  ampere  is  such  a  current  as  will 
deposit  .00032959  grammes,  or  .005084  grains,  of  copper  per 
second  on  the  plate  of  a  copper  voltameter  (See  Voltameter), 
or  which  will  decompose  .00009326  grammes,  or  .001439 
grains,  of  dilute  sulphuric  acid  per  second,  or  pure  sulphuric 
acid  at  59°  F.  diluted  with  about  fifteen  percent,  of  water,  that 
is,  dilute  sulphuric  acid  of  Sp.  Gr.  of  about  1.1. 

Ampere-Hotir,  Ampere-Minute,  Ampere-Sec- 
ond.— One  ampere  flowing  for  one  hour,  one  minute,  or  one 
second  respectively. 

The  ampere-hour  is  in  reality  a  unit  of  quantity  like  the 
coulomb.  It  is  used  in  the  service  of  electric  currents,  and 
is  equal  to  the  product  of  the  current  delivered,  by  the  time 
during  which  it  is  delivered.  The  ampere-hour  is  not  a  meas- 
ure of  energy,  but  when  combined  with  the  volt,  and  ex- 
pressed in  watt-hours,  it  is  a  measure  of  energy. 

The  storing  capacity  of  accumulators  is  generally  given  in 
ampere-hours.  The  same  is  true  of  primary  batteries. 

One  coulomb  =  .0002778  ampere-hours. 

One  ampere-hour  =  3, 600  coulombs.  (See  Watt-Hour,  Watt- 
Minute,  Watt-Second.) 

Ampere-Meter ;  Am-meter.— A  form  of  galvanometer 
originally  designed  by  Ayrton  and  Perry  to  indicate  directly, 


26  A  DICTIONARY   OF  ELECTRICAL 

the  strength  of  current  passing  in  amperes.     (See  Galvano- 
meter.) 

Like  all  galvanometers,  the  strength  of  current  passing, 
i.  e.,  the  number  of  amperes,  is  indicated  by  the  deflection  of  a 
magnetic  needle  placed  inside  or  over  a  coil  of  insulated  wire 
through  which  the  current  to  be  measured  is  passed. 

In  the  form  originally  devised  by  Ayrton  and  Perry,  the 
needle  came  to  rest  almost  immediately,  or  was  dead  beat  in 
action.  (See  Dead  Beat.)  It  moved  through  the.  field  of  a 
permanent  magnet.  The  instrument  was  furnished  with  a 
number  of  coils  of  insulated  wire,  which  could  be  connected 
either  in  series  or  in  middle-arc  by  means  of  a  commutator, 
thus  permitting  the  scale  reading  to  be  verified  or  calibrated 
by  the  use  of  a  single  voltaic  cell.  (See  Circuits,  Varieties 
of.  Commutator.  Calibration,  Absolute  or  Relative,  of  Instru- 
ment.) In  this  case  the  coils  were  turned  to  series,  and  the 
plug  to  the  left  pulled  out,  thus  introducing  a  resistance  of 
one  ohm. 

Fig.  13,  represents  a  form 
of  Ayrton  and  Perry's  Am- 
meter. A  device  called  a 
I  commutator  for  connect- 
ing the  coils  either  in  series 
or  parallel  is  shown  at  C. 
Binding-posts  are  provided 
at  P,  PS,  and  S.  The  dy- 
namo terminals  are  con- 
nected at  the  posts  P,  P, 

Fig  }3  and  the  current  will  pass 

only  when  the  coils  are 
in  multiple,  thus  avoiding  accidental  burning  of  the  coils. 
In  this  case  the  entire  current  to  be  measured  passes  through 
the  coils  so  coupled.  The  posts  S,  and  PS  are  for  connect- 
ing the  single  battery  cell  current. 
A  great  variety  of  ampere-meters,  or  am-meters,  have  been 


WORDS,   TERMS  AND   PHRASES.  27 

devised.  They  are  nearly  all,  however,  constructed  on  es- 
sentially the  same  general  principles. 

Ampere-Feet.— The  product  of  the  current  in  amperes 
by  the  distance  in  feet  through  which  that  current  passes. 

It  has  been  suggested  that  the  term  ampere-feet  should  be 
employed  in  expressing  the  strength  of  electro-magnetism, 
in  the  field  magnets  of  dynamo-electric  machines  or  other 
similar  apparatus. 

Ampere-Turn*,  or  Ampere- Windings.— A  single 
turn  or  winding  through  which  one  ampere  passes. 

The  number  of  amperes  multiplied  by  the  number  of  wind- 
ings or  turns  of  wire  in  a  coil  give  the  total  number  of  am- 
pere-turns in  the  coil.  The  magnetism  developed  by  a  given 
number  of  ampere-turns  is  independent  of  the  current  or  of 
the  number  of  turns  of  wire,  as  long  as  the  product  of  the 
amperes  and  the  turns  remains  the  same.  That  is  to  say,  tho 
same  amount  of  magnetism  can  be  obtained  by  the  use  of  many 
windings  and  a  small  current,  as  in  shunt  dynamos,  or  by  a 
few  turns  and  a  proportionally  large  current,  as  in  series 
dynamos.  (See  Dynamo- Electric  Machines.) 

Ampere-Volt.— A  watt,  or  .\,.  of  a  horse-power. 

This  term  is  generally  written  volt-ampere.  (See  Volt- Am- 
pere.) 

Auiperiiiii  Currents.— The  electric  currents  that  are 
assumed  in  the  Amperian  theory  of  magnetism  to  How  around 
the  molecules  of  a  magnet.  (See  Magnetism,  Amperian 
Theory  or  Hypothesis  of.) 

The  Amperian  currents  are  to  be  distinguished  from  the 
Eddy,  Foucault,  or  Parasitical  Currents,  since,  unlike  them, 
they  are  directed  so  as  to  produce  useful  effects.  (See  Cur- 
rents, Eddy,  Foucault,  Parasitical.) 

Amplitude  of  Vibration  or  Wave.— The  ratio  that 
exists  in  any  sound-wave  between  the  degree  of  condensation 
and  rarefaction  of  the  air  or  other  medium  in  which  the  wave 
is  propagated. 


28  A  DICTIONARY  OF  ELECTRICAL 

The  amplitude  of  a  wave  is  dependent  on  the  amount  of 
energy  charged  on  the  medium  in  which  the  vibration  or  wave 
is  produced. 

A  vibration  or  wave  is  a  to-and-fro  motion  produced  in  an 
elastic  material  or  medium  by  the  action  thereon  of  energy. 
Sound,  light  and  heat  are  effects  produced  by  the  action  of 
vibrations  or  waves,  which,  in  the  case  of  sound,  are  set  up 
in  the  air,  and,  in  that  of  light  and  heat,  in  a  highly  tenuous 
medium  called  the  luminiferous  ether. 

As  the  amplitude  of  a  sound  wave  increases,  the  loudness 
or  intensity  of  the  sound  increases.  As  the  amplitude  of  the 
ether-wave  increases,  the  brilliancy  of  the  light  or  the  inten- 
sity of  the  heat  increases. 

Let  A  C,  Fig.  14,  represent  an  elastic  cord  or  string  tightly 
stretched  between  A  and  C.  If  the  string  be  plucked  by  the 
finger,  it  will  move  to  and  fro,  as  shown  by  the  dotted  lines. 
Each  to-and-fro  motion  is  called  a  vibration.  The  vertical 


E 

Fig.  IU. 

distance  B  D,  or  B  E,  represents  the  amplitude  of  the 
vibration,  and  the  sound  produced  is  louder,  the  greater  the 
amount  of  energy  with  which  the  string  has  been  plucked, 
or,  in  other  words,  the  greater  the  value  of  B  D,  or  B  E. 

Vibrations  assume  various  forms  in  solid  or  fluid  media,  but 
in  all  cases  the  amplitude  will  be  proportional  fro  the  amount 
of  energy  that  causes  the  vibration. 

Analogous  Pole.— (See  Pole,  Analogous.) 

Analysis. — The  determination  of  the  composition  of  a 
compound  substance  by  separating  it  into  the  simple  sub- 
stances of  which  it  is  composed. 

Chemical  analysis  is  qualitative  when  it  simply  ascertains 


WORDS,   TERMS  AND  PHRASES.  3d 

the  kinds  of  elementary  substances  present.  It  is  quanti- 
tative when  it  ascertains  the  relative  proportions  in  which  the 
different  components  enter  into  the  compound. 

Analysis),  Electric Ascertaining  the  composi- 
tion of  a  substance  by  electrical  means. 

Various  processes  have  been  proposed  for  electric  analysis  ; 
they  consist  essentially  in  decomposing  the  substance  by 
means  of  electric  currents,  and  are  either  qualitative  or 
quantitative.  (See  Electrolysis,  or  Electrolytic  Decomposi- 
tion.) 

Anelcctrotomis. — In  electro  thei-apeutics,  the  decreased 
functional  activity  that  occurs  in  a  nerve  in  the  neighbor- 
hood of  the  anode,  or  positive  electrode.  (See  Electro- 
tonus.) 

Angle. — The  deviation  in  direction  between  two  lines. 

Ang'les  are  measured  by  arcs  of  cir-      £v  & 

cles.  The  angle  at  B  A  C,  Fig.  15,  is  the 
deviation  of  the  straight  line  A  B  from 
A  C.  In  reading  the  lettering  of  an 
angle  the  letter  placed  in  the  middle 
indicates  the  angle  referred  to.  Tims 
BAG,  means  the  angle  between  A  B  ' 
and  A  C ;  B  A  D,  the  angle  between 

B  A  and  A  D.  Angles  are  valued  in  degrees,  there  being  360 
degrees  in  an  entire  circumference  or  circle.  Degrees  are 
indicated  thus  :  90°,  or  ninety  degrees. 

The  complement  of  an  angle  is  what  the  angle  needs  to 
make  its  value  90°,  or  a  right  angle.  Thus  B  A  E,  is  the 
complement  of  the  angle  E  A  D,  since  BAE-|-EAD  =  90°. 

The  supplement  of  an  angle  is  what  the  angle  needs  to  make 
its  value  180°,  or  two  right  angles.  Thus  E  A  C  is  the  supple- 
ment of  BAD,  because  EA  D-f  E  A  C  =  180°,  or  two  right 
angles. 

Angle   of  Declination   or  Variation.— The  angle 


30  A   DICTIONARY  OF  ELECTRICAL 

which  measures  the  deviation  of  the  magnetic  needle  from 
the  east  or  west  of  the  true  geographical  north. 

Thus,  in  Fig.  16,  if  N  S  represents  the 
true  north  and  south  line,  the  angle  of 
declination  is  N  O  A,  and  the  sign  of  the 
variation  is  east,  because  the  deviation  of 
I  E  the  needle  is  toward  the  east.  For  further 
details  see  Declination  or  Variation  of 
Magnetic  Needle. 

Angle  of  Dip  or  Inclination.— 
The  angle  which  a  magnetic  needle,  free 
to  move  in  a  vertical  and  horizontal 
plane,  makes  with  a  horizontal  line  passing  through  its  point 
of  support. 

A  magnetic  needle  supported  at  its  centre  of  gravity,  and 
capable  of  moving  freely  in  a  vertical  as  well  as  in  a  horizontal 
plane,  does  not  retain  a  horizontal  position  at  all  parts  of  the 
earth's  surface. 

The  angle  which  marks  its  deviation  from  the  horizontal 
position  is  called  the  angle  of  dip  or  inclination.  For  further 
details  see  Dip,  Magnetic. 

Angle  of  L.ag.— The  angle  through  which  the  axis  of 
magnetism  of  the  armature  of  a  dynamo-electric  machine  is 
shifted  by  reason  of  the  resistance  its  core  offers  to  sudden 
reversals  of  magnetization. 

A  bi-polar  armature  of  a  dynamo-electric  machine,  has  its 
magnetism  reversed  twice  in  every  rotation.  The  iron  of  the 
core  resists  this  magnetic  reversal.  The  result  of  this  resist- 
ance is  to  shift  the  axis  of  magnetization  in  the  direction  of 
rotation.  The  angle  through  which  the  axis  has  thereby  been 
shifted  is  called  the  angle  of  lag.  This  term,  angle  of  lag,  is 
sometimes  incorrectly  applied  so  as  to  include  a  similar  result 
produced  by  the  magnetization  due  to  the  armature  current 
itself.  It  is  this  latter  action  which,  in  armatures  with  soft 


WORDS,   TERMS  AND  PHRASES.  31 

iron  cores,  is  the  main  cause  of  the  angle  of  lead.     (See  Angle 
of  Lead.    Lead  of  Brushes.) 

Angle  of  Lead. — The  angular  deviation  from  the  normal 
position  which  must  be  given  to  the  collecting  brushes  on  the 
commutator  cylinder  of  a  dynamo-electric  machine,  in  order 
to  avoid  destructive  burning.  (See  Burning  at  Commutator.) 

The  necessity  for  giving  Ihe  collecting  brushes  a  lead,  arises 
both  from  the  magnetic  lag,  and  the  distortion  of  the  field 
of  the  machine  by  the  magnetization  of  the  armature  current. 
The  angle  of  lead  is,  therefore,  equal  to  the  sum  of  the  angle 
of  lag  and  the  angular  distortion  due  to  the  magnetization 
produced  by  the  armature  current. 

Angular  Velocity.— The  velocity  of  a  body  moving  in  a 
circular  path,  measured,  not,  as  usual,  by  the  length  of  its 
path  divided  by  the  time,  but  by  the  angle  that  path  subtends 
times  the  length  of  the  radius,  divided  by  the  time. 

If  r  is  the  radius,   a    the  angle,    and  t  the    time,    then 

ra 
Angular  Velocity  =  — . 

Unit  Angle  is  that  angle  subtended  by  a  part  of  the  circum- 
ference equal  to  the  length  of  the  radius,  or  57°  17'  44".8  nearly 
(Daniell). 

Unit  Angular  Velocity  is  the  velocity  under  which  a  particle 
moving  in  a  circular  path  whose  radius  equals  unity  would 
traverse  unit  angle  in  vmit  time. 

Animal  Electricity.— Electricity  produced  during  life  in 
the  bodies  of  certain  animals,  such  as  the  Torpedo,  the  Gym- 
notus,  and  the  Silurus. 

Some  of  these  animals,  when  of  full  size,  are  able  to  give 
very  severe  shocks,  and  use  this  curious  power  as  a  means  of 
defence  against  their  enemies. 

All  animals  probably  produce  electricity.  If  the  spinal  cord 
of  a  recently  killed  frog  be  brought  into  contact  with  the 
muscles  of  the  thigh,  a  contraction  will  ensue  (Matteucci). 


32  A  DICTIONARY  OP  ELECTRICAL 

The  nerve  and  muscle  of  a  frog,  connected  by  a  water  con- 
tact with  a  sufficiently  delicate  galvanometer,  show  the 
presence  of  a  current  that  may  last  several  hours.  Du  Bois- 
Reymond  showed  that  the  ends  of  a  section  of  muscular 
fibres  are  negative,  and  their  sides  positive,  and  has  obtained 
a  current  by  suitably  connecting  them. 

All  muscular  contractions  apparently  produce  electric  cur- 
rents. 

Anion.— The  electro-negative  radical  of  a  molecule. 

Literally,  the  term  ion  signifies  a  group  of  wandering  atoms. 
An  anion  is  that  group  of  atoms  of  an  electrically  decomposed 
or  electrolysed  molecule  which  appears  at  the  anode.  (See 
Electrolysis.  Anode) 

As  the  anode  is  connected  with  the  electro-positive  termi- 
nal of  a  batteiy  or  source,  the  anion  is  the  electro-negative 
radical  or  group  of  atoms,  and  therefore  appears  at  the  electro- 
positive terminal.  A  kathion,  or  electro-positive  radical,  ap- 
pears at  the  kathode,  which  is  connected  with  the  electro- 
negative terminal  of  the  battery.  Oxygen  and  chlorine  are 
anions.  Hydrogen  and  the  metals  are  kathions. 

Anisotropic  Conductor.— A  conductor  which,  though 
homogeneous  in  structure  like  crystalline  bodies,  has  different 
physical  properties  in  different  directions,  just  as  crystals 
have  different  properties  in  the  direction  of  the  different 
crystalline  axes. 

Anisotropic  conductors  possess  different  powers  of  electric 
conduction  in  different  directions.  They  differ  in  this  respect 
from  isotropic  conductors.  (See  Isotropic  Conductor.) 

Anisotropic  medium.— A  medium,  homogeneous  in 
structure  like  crystalline  bodies,  possessing  different  powers 
of  specific  inductive  capacity  in  different  directions. 

The  term  is  used  to  distinguish  it  from  an  isotropic  medium. 
(See  Isotfopic  Medium.) 

Aliode. — The  conductor  or  plate  of  a  decomposition  cell 


WORDS,   TERMS  AND  PHRASES.  33 

connected  with  the  positive  terminal  of  a  battery,  or  other 
electric  source. 

That  terminal  of  an  electric  source  out  of  which  the  current 
flows  into  the  liquid  of  a  decomposition  cell  or  voltameter  is 
culled  the  anode.  That  terminal  of  an  electric  source  into 
which  the  current  flows  from  a  decomposition  cell  or  volta- 
meter is  called  the  kathode, 

The  anode  is  connected  with  the  carbon  or  positive  ter- 
minal  of  a  voltaic  battery,  and  the  kathode  with  the  zinc,  or 
negative  terminal.  Therefore  the  word  anode  has  been  used 
to  signify  the  positive  terminal  of  an  electric  source,  and 
kathode,  the  negative  terminal,  and  in  this  sense  is  employed 
generally  in  electro  therapeutics.  It  is  preferable,  however, 
to  restrict  the  words  anode  and  kathode  to  those  terminals  of 
a  source  at  which  electrolysis  is  taking  place. 

The  terms  anode  and  kathode  in  reality  refer  to  the  electro- 
receptive  devices  through  which  the  current  flows.  Since  it 
is  assumed  that  the  current  flows  out  of  a  source  from  its 
positive  pole  or  terminal,  and  back  to  the  source  at  its  nega- 
tive pole  or  terminal,  that  pole  of  any  device  connected  with 
the  positive  pole  of  a  source  is  the  part  by  or  at  which  the 
current  enters,  and  that  connected  with  the  negative  pole,  the 
part  at  which  it  leaves.  Hence,  probably,  the  change  in  the 
use  of  the  words  already  referred  to. 

Since  the  anion,  or  the  electro-negative  radical,  appeal's  at 
the  anode,  it  is  the  anode  of  an  electro-plating  bath,  or  the 
plate  connected  with  the  positive  terminal  of  the  source  that 
is  dissolved. 

When  the  term  anode  was  first  proposed  by  Faraday,  vol- 
taic batteries  were  the  only  available  electric  source,  and 
the  term  referred  only  to  the  positive  terminal  of  a  voltaic 
battery  when  placed  in  an  electrolyte. 

Anodic  Opening  Contraction.— The  muscular  con- 
traction observed  on  the  opening  of  a  voltaic  circuit,  the 
anode  of  which  is  placed  over  a  nerve,  and  the  kathode  at  some 
other  part  of  the  body. 


A  DICTIONARY   OF   ELECTRICAL 


This  term  is  generally  written  A.  O.  C.  When  the  anode 
is  placed  over  a  nerve  and  a  weak  current  is  employed,  if  the 
circuit  be  kept  closed  for  a  few  minutes,  it  will  be  noticed 
that,  on  opening,  the  contraction  will  be  much  greater  than 
if  it  had  been  opened  after  being  closed  for  only  a  few  seconds. 
The  effect  of  the  A.  O.  C.  therefore  depends  not  only  on  the 
current  strength  but  also  on  the  time  during  which  the  cur- 
rent has  passed  through  the  nerve. 

Annunciator,  Electro-magnetic An  electric 

device  for  automatically  indicating  the  places  at  which  one  or 
more  electric  contacts  have  been  closed. 

Annunciators  are  employed  for  a  variety  of  purposes.  In 
hotels  they  are  used  for  indicating  the  number  of  a  room  the 
occupant  of  which  desires  some  sei'vice  which  he  signifies  by 
pushing  a  button,  thus  closing  an  electric  circuit.  This  is  in- 
dicated or  announced  on  the  annunciator  by  the  falling  of  a 
drop  on  which  is  printed  a 
number  corresponding  with  the 
room,  and  the  ringing  of  a  bell 
to  notify  the  attendant.  The 
number  is  released  by  the  action 
of  the  armature  of  an  electro- 
magnet. The  drops  are  replaced 
in  their  former  position  by  some 
mechanical  device  operated  by 
the  hand.  In  the  place  of  a  drop 
a  needle  is  sometimes  used, 
which  points  to  the  number  sig- 
nalling, by  the  attraction  of  the 
armature  of  an  electro-magnet. 
Annunciators  for  houses,  bur- 
glar-alarms, fire-alarms,  eleva- 
tors, etc.,  are  of  the  same  g'eneral 
construction. 
Fig.  17,  shows  an  annunciator  suitable  for  use  in  hotels. 


WORDS,,  TERMS  AND  PHRASES. 


35 


The  numbers  28  and  85  are  represented  as  having  been 
dropped  by  the  closing  of  the  circuit  connected  with  them. 

Anomalous  Magnet. — A  magnet  possessing  more  than 
two  free  poles. 

There  is  no  such  thing  as  a  unipolar  magnet.  All  magnets 
have  two  poles.  Sometimes,  however,  several  magnets  are 
so  grouped  that  there  appear  to  be  more  than  two  poles  in  the 
same  magnet. 


Fig.  18. 

Thus,  in  Fig.  18,  the  magnet  ABC  appears  to  possess 
three  poles,  two  positive  poles  at  A  and  C,  and  a  central 
negative  pole  at  B. 

It  is  clear,  however,  that  the  central  pole  is  in  reality  formed 
of  two  juxtaposed  negative  poles,  and  that  ABC  actually 
consists  of  two  magnets  with  two  poles  to  each. 


The  magnet  A  B  C  D,  Fig.  19,  which  in  like  manner  ap- 
pears to  possess  four  separate  poles,  in  reality  is  formed  of 
three  magnets  with  two  poles  to  each. 

Since  unlike  magnetic  poles  neutralize  each  other,  it  is  clear 
that  only  similar  poles  can  thus  be  placed  together  in  order  to 
produce  additional  magnet  poles. 


36  A  DICTIONARY  OF  ELECTRICAL, 

The  six-pointed  star  shown 
in  Fig.  20,  is  an  anomalous 
magnet  with  apparently  seven 
poles.  The  formation  of  the 
central  N-pole,  as  is  evident 
e  from  an  inspection  of  the 
drawing,  is  due  to  the  six 
separate  north  poles,  n,  n,  n, 
n,  n,  n,  of  the  six  separate 
magnets  Sn,  Sn,  etc.  Such 
a  magnet  would  be  formed 

S      Fig  20  '    S  by  touching  the  star  at  the 

point  N  with  the  S-pole  of  a  sufficiently  powerful  magnet. 

These  extra  poles  are  sometimes  called  consequent  poles. 
Their  presence  may  be  shown  by  means  of  a  compass  needle, 
or  by  rolling  the  magnet  in  iron  filings,  which  collect  on  the 
poles. 

Anti-Induction  Conductor.— A  conductor  so  con- 
structed as  to  avoid  injurious  inductive  effects  from  neighbor- 
ing telegraphic  or  electric  light  and  power  circuits. 

Such  anti-induction  conductors  generally  consist  of  a  con- 
ductor and  a  metallic  shield  surrounding  the  conductor,  which 
is  supposed  to  prevent  induction  taking  place  in  the  wire  itself. 
The  anti-induction  conductor  sometimes  consists  of  a  con- 
ductor enclosed  by  some  form  of  metallic  shield,  which  is 
supposed  to  prevent  the  action  of  electrostatic  induction. 
Antilogous  Pole.— (See  Pole,  Antilogous.) 
Anvil. — The  front  contact  of  a  telegraphic  key  that  limits 
its  motion  in  one  direction.     (See  Telegraphic  Key.) 

A.  O.  €.— A  contraction  used  in  medical  electricity  for 
Anodic  Opening  Contraction.  (See  Anodic  Opening  Con- 
traction.) 

Apparatus,    Interlocking; (See    Interlocking 

Apparatus,    Block  System  for  Railroads.) 


WORDS,  TERMS  AND  PHRASES.  37 

Arago's  Disc. — (See  Disc,  Arago's.) 

Arc  Lamp,  Electric (See  Lamp,  Arc,  Electric.) 

Arc,  metallic A  voltaic  arc  formed  between  me- 
tallic electrodes. 

When  the  voltaic  arc  is  formed  between  metallic  electrodes 
instead  of  carbon  electrodes,  a  naming  arc  is  obtained,  the  color 
of  which  is  characteristic  of  the  burning  metal ;  thus  copper 
forms  a  brilliant  green  arc.  The  metallic  arc,  as  a  rule,  is 
much  longer  than  an  arc  with  the  same  current  taken  between 
carbon  electrodes. 

Arc  Micrometer. — (See  Micrometer,  Arc.) 

Arc,  Voltaic The  brilliant  arc  or  bow  of  light 

that  appears  between  the  carbon  electrodes  or  terminals  of  a 
sufficiently  powerful  source  of  electricity. 

The  source  of  light  in  the  electric  arc  lamp. 

It  is  called  the  voltaic  arc  because  it  was  first  obtained  by 
the  use  of  the  battery  invented  by  Volta.  The  term  arc  was 
given  to  it  from  the  shape  of  the  luminous  bow  or  arc  formed 
between  the  carbons. 

To  form  the  voltaic  arc  the  carbon  electrodes  are  first  placed 
in  contact  and  then  gradually  separated.  A  brilliant  arc  of 
flame  is  formed  between  them,  which  consists  mainly  of  vola- 
tilized carbon.  The  electrodes  are  therefore  consumed,  first, 
by  actual  combination  with  the  oxygen  of  the  air,  and,  second, 
by  volatilization  under  the  combined  influence  of  the  electric 
current  and  the  i  ntense  heat. 

As  a  result  of  the  formation  of  the  arc,  a  tiny  crater  is  formed 
in  the  end  of  the  positive  carbon,  and  appears  to  mark  the 
point  out  of  which  the  greater  part  of  the  current  flows. 

The  crater  is  due  to  the  greater  volatilization  of  the  elect- 
rode at  this  point  than  elsewhere.  It  marks  the  position  of 
greatest  temperature  of  the  electrodes,  and  is  the  main  source 
of  the  light  of  the  ai-c.  When,  therefore,  the  voltaic  arc  is 
employed  for  the  purposes  of  illumination  with  vertically  op- 


88  A  DICTIONARY  OP  ELECTRICAL 

posed  carbons,  the  positive  carbon  should  be  made  the  upper 
carbon,  so  that  the  focus  of  greatest  intensity  of  the  light  may 
be  favorably  situated  for  illumination  of  the  space  below  the 
lamp. 

The  crater  in  the  end  of  the  positive 
carbon  is  seen  in  Fig.  21.  On  the 
opposed  end  of  the  negative  carbon 
a  projection  or  nipple  is  formed  by 
the  deposit  of  the  electrically  volatil- 
ized carbon.  The  rounded  masses  or 
globules  that  appear  on  the  surface 
of  the  electrodes  are  due  to  deposits 
of  molten  foreign  matters  in  the  car- 
bon. 

The  carbon,  both  of  the  crater  and 
its  opposed  nipple,  is  converted  into 
pure,  soft  graphite. 

***•"'  Arc,  Voltaic Rcsi§tanc® 

of. — The  resistance  offered  by  the  voltaic  arc  to  the  passage 
of  the  current. 

Like  all  conductors,  the  ohmic  resistance  of  the  arc  increases 
with  its  length,  and  decreases  with  its  area  of  cross-section. 
An  increase  of  temperature  decreases  the  resistance  of  the 
voltaic  arc. 

The  total  apparent  resistance  of  the  voltaic  arc  is  composed 
of  two  parts,  viz.  : 

(1.)  The  true  ohmic  resistance.  (See  Ohmic  or  True  Resist- 
ance.) 

(2.)  The  counter  electro-motive  force,  or  spurious  resistance. 
(See  Spurious  Resistance.) 

Areometer  or  Hydrometer.— An  instrument  for  de- 
terming  the  specific  gravity  of  a  liquid. 

A  common  form  of  hydrometer  consists,  as  shown  in  Fig. 
22,  of  a  closed  glass  tube,  provided  with  a  bulb,  and  filled  at 
the  lower  end  with  mercury  or  shot.  When  placed  in  different 


WORDS,   TERMS  AND  PHRASES. 


liquids,  it  floats  with  part  of  the  tube  out  of  the  liquid. 
The  lighter  the  liquid  the  smaller  is  the  portion  that 
remains  out  of  the  liquid  when  the  instrument  floats. 
The  specific  gravity  is  determined  by  observing  the 
depth  to  which  it  sinks  when  placed  in  different  liquids, 
as  compared  with  the  depth  it  sinks  when  placed  in 
water. 

Argaml  Lighter,  Electric An  electric 

device  for  lighting  the  gas  by  pulling  a  pendant  B, 
Fig.  23,  after  it  is  turned  on  by  hand. 

The  gas  is  ignited  by  means  of  an  electric  spark 
obtained  from  the  extra  current  of  a  spark  coil.  (See 
Current,  Extra). 

Argaiid 
Electric- 


Valve     Burner, 

A     burner    in 


which  the  pulling  of  the  ball  B, 
Fig.   24,  turns  on  and  lights  the 
gas,  while  the  motion  of  the  slide 
extinguishes  it. 

In  some  forms  of 
argand  burner,  a 
second  pulling  of  the 
ball  B,  turns  off  the 
gas. 

Armature.  —  A 
mass  of  iron  or  other 
magnetizable  materi- 
al placed  on  or  near 
the  pole  or  poles  of  a 
Fig.  23.  magnet. 

In  the  case  of  a  permanent  magnet  the  armature,  when 
used  as  a  keeper,  is  of  soft  iron  and  is  placed  directly  on  the 
magnet  poles.  In  this  case  it  preserves  or  keeps  the 
magnetism  by  closing  the  lines  of  magnetic  force  of  the 


40  A  DICTIONARY  OF  ELECTRICAL 

magnet  through  the  soft  iron  of  the  armature,  and  is  then 
called  a  keeper.  In  the  case  of  an  electro-magnet,  the  arma- 
ture is  placed  near  the  poles,  and  is  moved  toward  them 
whenever  the  magnet  is  energized  hy  the  passage  of  the  cur- 
rent. This  movement  is  made  against  the  action  of  a  spring 
or  weights,  so  that  on  the  loss  of  magnetism  by  the  magnet, 
the  armature  moves  in  the  opposite  direction.  (See  Magnet, 
Permanent.  Keeper  of  Magnet.} 

When  the  armature  is  of  soft  iron  it  moves  towards  the 
magnet  on  the  completion  of  the  circuit  through  the  coils,  no 
matter  in  what  direction  the  current  flows,  and  is  then  called 
a  non-polarized  armature.  When  made  of  steel,  or  of  another 
electro-magnet,  it  moves  towards  or  from  the  poles,  according 
to  whether  its  poles  are  of  the  same  or  of  different  polarity. 
Such  an  armature  is  called  a  polarized  armature.  (See  Arm- 
ature, Polarized.) 

Armature,  Dynamo The  part  of  a  dynamo- 
electric  machine  in  which  the  useful  currents  are  gene- 
rated. 

The  armature  usually  consists  of  a  series  of  coils  of  insu- 
lated wire  or  conductors,  that  are  wrapped  around  or  grouped 
on  a  central  core  of  iron.  The  movement  of  these  wires  or 
conductors  through  the  magnetic  field  of  the  machine  pro- 
duces an  electric  current  by  means  of  the  electro-motive  forces 
so  generated.  Sometimes  the  field  is  rotated ;  sometimes 
both  armature  and  field  rotate. 

The  armatures  of  dynamo-electric  machines  are  of  a  great 
variety  of  forms.  They  may  for  convenience  be  arranged  under 
the  following  heads,  viz.: 

Cylindrical  or  drum  armatures,  disc  armatures,  pole  or 
radial  armatures,  ring  armatures,  and  spherical  armatures. 
For  further  particulars  see  above  terms.  Armatures  are 
also  divided  into  classes  according  to  the  character  of  the 
magnetic  field  through  which  they  move — into  uni-polar,  b>.- 


WORDS,   TERMS  AND  PHRASES.  41 

polar,  and  multi-polar  armatures.     (See  Dynamo-Electric  Ma- 
chines.) 

The  term  armature  as  applied  to  a  dynamo-electric  machine 
was  derived  from  the  fact  that  the  iron  core  acts  to  magnet- 
ically connect  the  two  poles  of  the  field  magnets  as  an  ordi- 
nary armature  does  the  poles  of  a  magnet. 

Armature*  of  Holtz  Machine.— A  badly  chosen  term 
for  the  pieces  of  paper  on  the  stationary  plate  of  the  Holtz  and 
other  similar  machines. 

Armature,  Polarized An  armature  that  pos- 
sesses a  polarity  independent  of  that  imparted  by  the  mag- 
net pole  near  which  it  is  placed. 

In  permanent  magnets  the  armatures  are  made  of  soft  iron, 
and  therefore,  by  induction,  become  of  a  polarity  opposite  to 
that  of  the  magnet  poles  that  lie  nearest  them.  They  have, 
therefore,  only  a  motion  of  attraction  towards  such  poles. 
(See  Induction,  Magnetic.) 

In  electro-magnets  the  armatures  may  either  be  made  of 
soft  iron,  in  which  case  they  are  attracted  only  on  the  passage 
of  the  current ;  or  they  may  be  formed  of  permanent  steel 
magnets,  or  may  be  electro-magnets  themselves,  in  which 
case  the  passage  of  the  current  through  the  coils  of  the  elec- 
tro-magnet or  electro-magnets  may  cause  either  attraction 
or  repulsion  according  as  the  adjacent  poles  are  of  opposite 
polarity  or  are  of  the  same  polarity. 

Armature  Coils,  Dynamo The  coils  of  wire 

or  conductors  on  the  armature  of  a  dynamo-electric  machine. 
(See  Dynamo-Electric  Machine,  Armature  Coils.) 

Armature   Core,  Dynamo The  core  of  iron 

around  or  on  which  the  armature  coils  are  wound  or  disposed. 
(See  Dynamo-Electric  Machine,  Armature  Cores.) 

Armor  of  Cable. — The  protecting  sheathing  or  metallic 
covering  on  the  outside  of  a  submarine  or  other  electric  cable. 


A  DICTIONARY  OP  ELECTRICAL 


Arms  of  Bridge  or  of  Elec- 
tric Balance.— The  electric  re- 
sistances in  an  apparatus  for  the 
p  measurement  of  resistance,  known 
as  Wheatstone's  Balance  or  Bridge. 
An  unknown  resistance,  such  for 
example,   as  that  at  D,  Fig.  25,  is 
measured  by  so  proportioning  the 
known    resistances    A,   C,   and  B, 
that  no  current  flows  through  the 
galvanometer  G,  across  the  circuit 
or  bridge  M  G  N.    (See  Balance,  Wheatstone's  Electric.) 

Arm§  or  Brackets),  Telegraphic—  —Arms  or 
brackets  placed  on  telegraph  poles  for  the  support  of  the  in- 
sulators. (See  Brackets  or  Arms,  Telegraphic.) 

Arrester,  Lightning  —  —A  device  for  protecting 
instruments  on  any  line  from  disturbance  by  lightning.  (See 
Lightning  Arrester.) 

Artificial  Carbons.— (See  Carbons,  Artificial.) 
Artificial  Illumination.— (See  Illumination,  Artificial.) 
Artificial  Magnets.— Any  magnet  not  formed  naturally. 
All  magnets  other  than  magnetic  iron  ore,  or  lodestone,  or 
meteoric  iron.     (See  Magnets,  Artificial.) 

Articulate  Speech. — The  successive  tones  of  the  human 
voice  that  are  necessary  to  produce  intelligible  words. 

The  phrase  articulate  speech  refers  to  the  joining  or  arti- 
culation of  the  successive  sounds  involved  in  speech.  The 
receiving  diaphragm  of  a  telephone  is  caused  to  reproduce 
the  articulate  speech  uttered  near  the  transmitting  diaphragm. 
Asphyxia. — Suspended  respiration,  resulting  eventually  in 
death,  from  the  non-aeration  of  the  blood. 

In  cases  of  insensibility  by  an  electric  shock  a  species  of 
asphyxia  is  sometimes  brought  about.  This  is  due,  probably, 
to  the  failure  of  the  nerves  and  muscles  that  carry  on  respira- 


WORDS,   TERMS  AND  PHRASES. 


4:! 


tion.     The  exact  manner  in  which  death  by  electrical  shock 
results  is  not  known.     (See  Death,  Electrical.} 

Astatic  Circuits.— (See  Circuits,  Astatic.) 

Astatic  Needle.— A  magnetic  needle  consisting  of  two 
magnets  rigidly  connected  together  and  placed  parallel  and 
directly  over  each  other,  with  opposite  poles  opposed. 

An  astatic  needle  is  shown 
in  Fig.  26.  The  two  mag- 
nets N  S,  and  S'  N',  are  di- 
rectly opposed  in  their  po- 
larities, and  are  rigidly  con- 
nected  together  by  means  of 
the  axis  a  a.  So  disposed, 
the  two  magnets  act  as  a 
very  weak  single  needle 
when  placed  in  a  magnetic 
field. 

Were  the  two  magnets  N  S,  and  S'  N',  of  exactly  equal 
strength,  with  their  poles  placed  in  exactly  the  same  ver- 
tical plane,  they  would  completely  neutralize  each  other,  and 
the  needle  would  have  no -directive  tendency.  Such  a  system 
would  form  an  Astatic  Pair  or  Couple. 

In  practice  it  is  impossible  to  do  this,  so  that  the  needle  has 
a  directive  tendency,  which  is  often  east  and  west. 

The  cause  of  the  east  and  west  directive  tendency  of  an 
unequally  balanced  astatic  system  will 
be  understood  from  an  inspection  of  Fig. 
27,  a.  Unless  the  two  needles,  n  s,  and 
s'n',  are  exactly  opposed,  they  will  form 
a  single  short  magnet,  N  N  N  N,  S  S  S  S, 
the  poles  of  which  are  on  the  sides  of 
the  needle.  The  system  pointing  with  Fig.  27,  a. 

its  sides  due  N.  and  S.  will  appear  to  have  an  east  and  west 
direction. 

An  astatic  needle  possesses  the  valuable  property  of  requir- 
ing a  smaller  force  to  deflect  it  than  a  single  needle  with 


A  DICTIONARY  OP  ELECTRICAL 


more  powerful  poles.     Its  magnetism  is  not  as  easily  lost  or 
reversed  as  that  of  a  weaker  magnet. 

The  principal  use  of  the  astatic  needle  is  in  the  astatic  gal- 
vanometer, in  which  the  needle  is  deflected  by  the  passage  of 
an  electric  current  through  a  conductor  placed  near  the 
needle.  Therefore  it  is  evident  that  one  of  the  needles  must 
be  outside  and  the  other  inside  the  coil.  In  the  most  sensi- 
tive form  of  galvanometer  there  is  also  a  coil  surrounding 
the  upper  needle,  the  two  coils  being  oppositely  connected,  so 
that  the  deflection  on  both  needles  is  in  the  same  direction, 
and  the  deflecting  power  is  equal  to  the  sum  of  the  two  coils, 
while  the  directive  power  of  the  needles  is  the  difference 
of  their  magnetic  intensities. 

In  the  astatic  system,  shown  in  Fig.  27,  the  current,  en- 
tering at  -f"  and  flowing  out  at  — , 
flows  above  one  needle,  S  N,  and  below 
the  other,  S'  N',  and  therefore  de- 
flects both  in  the  same  direction, 
since  their  poles  point  in  opposite  di- 
rections. 

In  some  galvanometers  a  varying 
degree  of  sensitiveness  is  obtained  by 
means  of  a  magnet,   called  a  com- 
pensating magnet  placed  on  an  axis 
fig.  27.  above  the  magnetic  needle.    As  the 

compensating  magnet  is  moved  towards  or  away  from  the 
needle  the  effect  of  the  earth's  field  is  varied,  and  with  it  the 
sensitiveness  of  the  galvanometer.  Such  a  magnet  may  form 
with  the  needle  an  astatic  system.  (See  Compensating  Magnet.) 
(See  Galvanometer,  Astatic.  Galvanometer,  Mirror.  Mul- 
tiplier, Schweigger's). 

Astatic  Galvanometer.— (See  Galvanometer,  Astatic.) 
A§tatic  System. — A  term  applied  to  an  astatic  combina- 
tion of  magnets. 

Asymptote.— A  curved  line  that  continually  approaches  a 
straight  line  but  never  meets  it. 


WORDS,   TERMS  AND  PHRASES.  45 

In  Fig.  28,  the  asymptote  C  D  continually    x 
approaches  the  line  y  z,  but  never  meets  it. 

This  mathematical  conception  is  like  a 
value  which,  although  constantly  reduced 
to  one-half  of  its  former  value,  is  never-  -y-  z 

theless  never  reduced  to  zero  or  no  value.  p\g.  23. 

Atmosphere,  The The  ocean  of  air  that  sur- 
rounds the  earth. 

The  atmosphere  is  composed,  by  weight,  of  oxygen  23  parts, 
nitrogen  77  parts,  carbonic  acid  gas  from  4  to  6  parts  in  10,000 
(or  about  a  cubic  inch  of  carbonic  acid  to  a  cubic  foot  of  air), 
together  with  varying  proportions  of  the  vapor  of  water. 

Besides  these  constant  ingredients  there  are  in  most  locali- 
ties a  number  of  other  substances  present  as  impurities. 

Atmosphere,  Ail A  pressure  of   a  gas  or  fluid 

equal  to  about  15  pounds  to  the  square  inch. 

At  the  level  of  the  sea  the  atmosphere  exerts  a  pressure  of 
about  15  pounds  avoirdupois  on  every  square  inch  of  the  earth's 
surface.  This  has  therefore  been  taken  as  a  unit  of  fluid 
pressure. 

For  more  accurate  measurements  pounds  to  the  square  inch 
are  employed. 

Atmospheric  pressures  are  measured  by  instruments  called 
Manometers.  (See  Manometer.) 

Atmosphere,    Residual The  trace  of   air  or 

other  gas  remaining  in  a  space  which  has  been  exhausted  of 
its  gaseous  contents  by  a  pump  or  other  means. 

It  is  next  to  impossible  to  remove  all  traces  of  air  from  a 
vessel  by  any  known  form  of  pump  or  other  appliance.  (See 
Vacuum,  Absolute.) 

Atmospheric  Electricity.— The  free  electricity  almost 
always  present  in  the  atmosphere. 

The  free  electricity  of  the  atmosphere  is  generally  positive, 
but  often  changes  to  negative  on  the  approach  of  fogs  and 


46  A  DICTIONARY  OF  ELECTRICAL 

clouds.  It  exists  in  greater  quantity  in  the  higher  regions  of 
the  air  than  near  the  earth's  surface.  It  is  stronger  when  the 
air  is  still  than  when  the  wind  is  blowing.  It  is  subject  to 
yearly  and  daily  changes  in  its  intensity,  being  stronger  in 
winter  than  in  summer,  and  at  the  middle  of  the  day  than 
either  at  the  beginning  or  the  close. 

Atmospheric  Electricity,  Origin  of The  ex- 
act cause  of  the  free  electricity  of  the  atmosphere  is  un- 
known. 

Peltier  ascribes  the  cause  of  the  free  electricity  of  the  at- 
mosphere to  a  negatively  excited  earth,  which  charges  the 
atmosphere  by  induction.  (See  Induction,  Electrostatic.) 
It  has  been  ascribed  to  the  evaporation  of  water ;  to  the  con- 
densation of  vapor ;  to  the  friction  of  the  wind  ;  to  the  motion 
of  terrestrial  objects  through  the  earth's  magnetic  field  ;  to  in- 
duction from  the  sun  and  other  heavenly  bodies ;  to  differ- 
ences of  temperature ;  to  combustion,  and  to  gradual  oxida- 
tion of  plant  and  animal  life.  It  is  possible  that  all  these 
causes  may  have  some  effect  in  producing  the  free  electricity 
of  the  atmosphere. 

Whatever  the  cause  of  the  free  electricity  of  the  atmosphere, 
there  can  be  but  little  doubt  that  it  is  to  the  condensation  of 
aqueous  vapor  that  the  high  difference  of  potential  of  the 
lightning  flash  is  due.  (See  Difference  of  Potential.)  As  the 
clouds  move  through  the  air  they  collect  the  free  electricity  on 
the  surfaces  of  the  minute  drops  of  water  of  which  clouds  are 
composed,  and  when  many  thousands  of  these  subsequently 
collect  m  larger  drops  the  difference  of  potential  is  enor- 
mously increased  in  consequence  of  the  equally  enormous  de- 
crease in  the  surface  of  the  single  drop  over  the  sum  of  the 
surfaces  of  the  coalescing  drops. 

Atom. — The  smallest  quantity  of  elementary  or  simple 
matter  that  can  exist. 

The  ultimate  particle  of  matter. 

Atom  means  that  which  cannot  be  cut.      It  is  generally 


WORDS,   TERMS  AND  PHRASES.  47 

agreed,  that  material  atoms  are  absolutely  unalterable  in  size, 
shape,  weight  and  density;  that  they  can  neither  be  cut, 
scratched,  flattened,  nor  distorted;  and  that  they  are  unaffected 
in  size,  density,  or  shape,  by  heat  or  cold,  or  by  any  known 
physical  force. 

Although  almost  inconceivably  small,  atoms  nevertheless 
possess  a  definite  size  and  mass.  According  to  Sir  Wm. 
Thomson,  the  smallest  visible  organic  particle,  1-4000  of  a 
millimetre  in  diameter,  will  contain  about  30,000,000  atoms. 

Atom,  Gramme  —  —Such  a  number  of  grammes  of 
any  elementary  substance  as  is  numerically  equal  to  the 
atomic  weight  of  the  substance. 

The  gramme-atom  of  a  substance  represents  the  number 
of  calories,  required  to  raise  the  temperature  of  one  gramme 
of  that  substance  through  1°  C.  (See  Heat,  Atomic.  Colo- 
rie.) 

Atomic  Attraction.— The  attraction  that  causes  the 
atoms  to  combine.  (See  Affinity.  Chemical ) 

Atomic  Energy.— (See  Energy,  Atomic.) 

Atomic  Heat.— (See  Heat,  Atomic.) 

Atomicity.— The  combining  capacity  of  the  atoms. 

The  relative  equivalence  of  the  atoms  or  their  atomic  ca- 
pacity. 

The  elementary  atoms  do  not  always  combine  atom  for 
atom.  Some  single  atoms  of  certain  elements  will  combine 
with  two,  three,  four,  or  even  more  atoms  of  another  ele- 
ment. 

The  value  of  the  atomic  capacity  of  an  atom  is  called  its 
quantivalence  or  valency. 

Elements  whose  atomic  capacity  is — 

One,  are  called  Monads,  or  Univalent. 
Two,  "  "  Dyads,  "  Bivalent. 
Three,  "  "  Triads,  "  Tnvalent. 
Four,  "  "  Tetrads,  "  Quadrivalent. 


48  A  DICTIONARY   OF  ELECTRICAL 

Five,   are  called  Pentads,     or  Quinquivalent. 
Six,        "        "      Hexads,       "  Sexivalent. 
Seven,  "        "      Heptads,     "  Septivalent. 

Atomic  Weight. — The  relative  weights  of  the  atoms  of 
elementary  substances. 

Since  the  atoms  are  assumed  to  be  indivisible,  they  must 
unite  or  combine  as  wholes  and  not  as  parts.  Although  we 
cannot  determine  exactly  the  actual  weights  of  the  different 
elementary  atoms,  yet  we  can  determine  their  relative 
weights  by  ascertaining  the  smallest  proportions  in  which 
any  two  atoms  that  combine  atom  for  atom  will  unite  with 
each  other.  Such' numbers  will  represent  the  relative  weights 
of  the  atoms. 

Atomization.— The  act  of  obtaining  liquids  in  a  spray  of 
finely  divided  particles. 

Atomizer. — An  apparatus  for  readily  obtaining  a  finely 
divided  jet  or  spray  of  liquid. 

A  jet  of  steam,  or  a  blast  of  a'r,  is  driven  across  the  open  end 
of  a  tube  thot  dips  below  the  surface  of  the  liquid  to  be  atom- 
ized. The  partial  vacuum  so  formed  draws  up  the  liquid, 
which  is  then  blown  by  the  current  into  a  tine  spray. 

Attracted  Disc  Electrometer.— (See  Electrometer, 
Attracted  Disc.) 

Attraction.— Literally  the  act  of  drawing  together. 

la  science,  a  name  for  a  series  of  unknown  causes  that 
effect,  Oi*  are  assumed  to  effect,  the  drawing  together  of 
atoms,  molecules  or  masses. 

The  phenomena  of  attraction  and  repulsion  underlie  nearly 
all  natural  phenomena.  While  their  effects  are  well  known, 
it  is  doubtful  if  anything  is  definitely  known  of  their  true 
causes. 

Attraction,  Atomic. (See  Affinity,  Chemical.} 

Attraction,  Electro-Dynamic The   mutual 


WORDS,   TERMS  AND  PHRASES. 


49 


attraction  of  electric  currents,  or  of  conductors  through  which 
electric  currents  are  passing.  (See  Electro- Dynamics.) 

Attraction,  Electro -Magnetic The  mutual 

attraction  of  the  unlike  poles  of  electro-magnets.  (See  Elec- 
tro-Magnet.) 

Attraction,  Electrostatic The  mutual  attrac- 
tion exerted  between  unlike  electric  charges,  or  bodies  pos- 
sessing unlike  electric  charges. 


Fig.  29.  Fig.  26 

For  example,  the  pith  ball  supported  on  an  insulated  string 
is  attracted,  as  shown  at  A,  Fig.  29,  by  a  bit  of  sulphur  which 
has  been  briskly  rubbed  by  a  piece  of  silk.  As  soon,  however, 
as  it  touches  the  sulphur  and  receives  a  charge,  it  is  repelled, 
as  shown  at  B,  Fig.  29a. 

These  attractions  and  repulsions  are  due  to  the  effects  of 
electrostatic  induction.  (See  Induction,  Electrostatic.) 

Attraction,  Magnetic The  mutual  attraction 

exerted  between  unlike  magnet  poles. 

Magnetic  attractions  and  repulsions  are  best  shown  by 
means  of  the  magnetic  needle  N  S,  shown  in  Fig.  30.  The 
N.  pole  of  an  approached  magnet  attracts  the  S.  pole  of 
the  needle  but  repels  the  N.  pole, 


A  DICTIONARY  OF  ELECTRICAL 


The  laws  of  magnetic  attraction  and  repulsion  may  be 
stated  as  follows,  viz. : 

(1)  Magnet  poles 
of  the  same  polarity 
repel  each  other. 

N  II  "Sfeta^w  (2)  Magnet  poles 

cf  unlike  names  at- 
tract each  other. 

A  small  bar  mag- 
net, N  S,  Fig.  31, 
laid  on  the  top  of  a 

light  vessel  floating-  on  the  surface  of  a 
liquid,  may  be  readily  employed  to  illus- 
trate the  laws  of  magnetic  attraction  and 
repulsion. 

so.  Attraction,  Mass  or  molar 

Gravitation. — The    mutual    attraction    exerted    between 
masses  of  matter.     (See  Gravitation.) 

Attraction,  Molecular 

The  mutual  attraction  exerted  between 
molecules. 

The  attraction  of  like  molecules,  or 
Fig.  si.  those  of  the  same  kind  of  matter,  is 

called  Cohesion  ;  that  of  unlike  molecules,  Adhesion. 

The  strength  of  iron  or  steel  is  due  to  the  cohesion  of  its 
molecules.  Paint  adheres  to  wood,  or  ink  to  paper,  by  the 
attraction  between  unlike  molecules. 

Audiphone.— A  thin  plate  of  hard  rubber  placed  in  the 
human  mouth  in  contact  with  the  teeth,  and  maintained  at  a 
certain  tension  by  strings  attached  to  one  of  its  edges,  for  the 
purpose  of  aiding  the  hearing. 

The  plate  is  so  held  that  the  sound-waves  from  a  speaker's 
voice  impinge  directly  against  its  flat  surface.  It  operates  by 
means  of  some  of  the  waves  being  transmitted  to  the  ear 
directly  through  the  bones  of  the  head. 


WORDS,   TERMS  AND  PHRASES.  51 

Aurora  Boreali§.— Literally,  the  Northern  Light.  Lu- 
minous sheets,  columns,  arches,  or  pillars  of  a  pale  flashing 
light,  generally  of  a  red  color,  seen  in  the  northern  heavens. 

The  auroral  light  assumes  a  great  variety  of  appearances,  to 
which  the  terms  auroral  arch,  bands,  coronce,  curtains  and 
streamers  are  applied. 

The  exact  cause  of  the  aurora  is  not  as  yet  known.  It 
would  appear,  however,  beyond  any  reasonable  doubt,  that 
the  auroral  flashes  are  due  to  the  passage  of  electrical  cur- 
rents or  discharges  through  the  upper,  and  therefore  rarer, 
regions  of  the  atmosphere.  The  intermittent  flashes  of 
light  are  probably  due  to  the  discharges  being  influenced  by 
the  earth's  magnetism. 

Auroras  are  frequently  accompanied  by  magnetic  storms. 
(See  Magnetic  Storms.) 

The  occurrence  of  auroras  is  often  simultaneous  with 
that  of  an  unusual  number  of  sun  spots.  Auroras  are  there- 
fore probably  connected  with  outbursts  of  the  solar  en- 
ergy. (See  Sun  Spots.) 

The  auroral  light  examined  by  the  spectroscope  gives  a 
spectrum  characteristic  of  luminous  gaseous  matter,  i.  e., 
contains  a  few  bright  lines  ;  but,  according  to  S.  P.  Thomp- 
son, this  spectrum  is  produced  by  matter  that  is  not  refer- 
able with  certainty  to  that  of  any  known  substance  on  the 
earth. 

Whatever  may  be  the  exact  cause  of  auroras,  their  ap- 
pearance is  almost  exactly  reproduced  by  the  passage  of  elec- 
tric discharges  through  vacuous  spaces.  (See  Geissler  Tubes.) 

Aurora  Australia.— The  Southern  Light.  A  name  given 
to  an  appearance  in  the  southern  heavens  similar  to  that  of 
the  Aurora  Borealis, 

Austral  Pole. — A  name  sometimes  employed  in  France 
for  the  north-seeking  pole  of  a  magnet. 

That  pole  of  a  magnet  which  points  to  the  earth's  geo- 
graphical north. 


A  DICTIONARY  OP   ELECTRICAL 


It  will  be  observed  that  the  French  regard  the  magnetism 
of  the  earth's  Northern  Hemisphere  as  north,  and  so  name  the 
north-seeking  pole  of  the  needle,  the  austral  or  south  pole. 

BATTERY  "^h6  south-seeking  pole 

"X.  of  the  magnet  is  some- 

\^      .,  ..^NS  times  called  the  boreal  or 

\     iF?  ?•    north  pole.    (See  Boreal 

Pole.) 

Automatic  Burner. 
— (See  Burner,  Auto- 
matic, Electric.) 

Automatic  Contact 
Breaker,  or  Auto- 
matic Hake-and- 
Break. — A  device  for 
causing  an  electric  cur- 
rent to  rapidly  make  and 
break  its  own  circuit. 

The  spring  c,   Fig.  32, 
Fig,  32.  carries  an    armature    of 

soft  iron,  B,  and  is  placed  in  a  circuit  in  such  a  manner  that 
the  circuit  is  closed  when  platinum  contacts  placed  on  the 
ends  of  D  and  B  touch  each  other.  In  this  case  the  arm- 
ature B  is  attracted  to  the  core  A,  of  the  electro-magnet, 
thus  breaking  the  circuit  and  causing  the  magnet  to  lose  its 
magnetism.  The  elasticity  of  the  spring  C,  causes  it  to  fly 
back  and  again  close  the  contacts,  thus  again  energizing  the 
electro-magnet  and  again  attracting  B,  and  breaking  the 
circuit.  The  makes  and  breaks  usually  follow  each  other  so 
rapidly  as  to  produce  a  musical  note.  (See  Alarm,  Electric.) 
Automatic  Cut-Out,  Electric —  —A  device  by 
means  of  which  an  electric  circuit  is  either  opened  or  short 
circuited,  whenever  the  current  passing  might  injure  the 
electro  receptive  devices.  (See  Short  Circuit.) 


WORDS,  TERMS  AND  PHRASES.  63 

The  safety  devices  for  arc  lights,  or  series  circuits,  differ  in 
their  construction  and  operation  from  those  for  incandescent 
lights,  or  multiple  circuits.  (See  Circuits,  Varieties  of. 
Safety  Device  for  Arc  Light  Circuits.  Safety  Catch.  Cut- 
out, Automatic.  Safety-Fuse.  Safety-Strip.  Fusible  Plug.) 

Automatic  Regulation.— Such  a  regulation  of  a  dy- 
namo-electric machine  as  will  preserve  constant  either  the 
current  or  the  electro-motive  force  generated  by  it. 

The  automatic  regulation  of  dynamo-electric  machines  may 
be  accomplished  in  the  following  ways,  viz. : 

(1)  By  a  Compound  Winding  of  the  machine. 

This  method  is  particularly  applicable  to  constant-potential 
machines.  By  this  winding  the  magnetic  strength  of  the  shunt- 
coils  is  constant,  while  that  of  the  series-coils  varies  proportion- 
ally to  the  load  on  the  machine.  The  series-coils  are  prefer- 
ably wound  close  to  the  poles  of  the  machine,  and  the  shunt- 
coils  nearer  the  yoke  of  the  magnets.  Custom,  however,  varies 
in  this  respect,  and  very  generally  the  shunt-coils  are  placed 
nearer  the  poles  than  the  series-coils.  (See  Compound- Wind- 
ing, Dynamo-Electric  Machines.) 

(2)  By  Shifting  the  Position  of  the  Collecting  Brushes. 

In  the  Thomson-Houston  system  the  current  is  kept  prac- 
tically constant  by  the  following  devices :  The  collecting 
brushes  are  fixed  to  levers  moved  by  the  regulator  magnet  R, 
as  shown  in  Fig.  33,  the  armature  of  which  is  provided  with 
an  opening  for  the  entrance  of  the  paraboloidal  pole  piece  A. 
A  dash-pot  is  provided  to  prevent  too  sudden  movement. 

When  the  current  is  normal,  the  coil  of  the  regulator  mag- 
net is  short-circuited  by  contact  points  at  S  T  which  act  as 
a  shunt  of  very  low  resistance.  These  contact-points  are 
operated  by  the  solenoid  coils  of  the  Controller  traversed  by 
the  main  current.  The  cores  of  this  solenoid  are  suspended 
by  a  spring.  When  the  current  becomes  too  strong  the  con- 
tact-point is  opened,  and  the  current,  traversing  the  coil  of 
the  regulator  magnet  A  attracts  its  armature,  which  shifts 


54 


A  DICTIONARY  OF  ELECTRICAL 


the  collecting  brushes  into  a  position  at  which  a  smaller  cur- 
rent is  taken  off.  A  carbon  shunt,  r,  of  high  resistance,  is 
provided  to  lessen  the  spark  at  the  contact-points  S  T,  which 
occurs  on  opening  the  circuit. 


Fig.  S3. 

In  operation  the  contact-points  are  continually  opening 
and  closing,  thus  maintaining  a  practically  constant  current 
in  the  external  circuit. 

(3)  By  the  Automatic  Variation  of  a  Resistance  shunting 
the  field  magnets  of  the  machine,  as  in  the  Brush  System. 

In  Fig.  34,  the  variable  resistance  C  forms  a  part  of  the 
shunt  circuit  around  the  field  magnets  F  M.  This  resistance  is 
formed  of  a  pile  of  carbon  plates.  On  an  increase  of  the  cur- 
rent, such,  for  example,  as  would  result  from  turning  out 
some  of  the  lamps,  the  electro-magnet  B,  placed  in  the  main 
circuit,  attracts  its  armature  A,  and,  compressing  the  pile  of 
carbon  plates  C,  lowers  their  resistance,  thus  diverting  a  pro- 
portionally larger  portion  of  the  current  from  the  field  magnet 
coils  F  M,  and  maintaining  the  current  practically  constant. 

In  some  machines  the  same  thing  is  done  by  hand,  but  this 
is  objectionable,  since  it  requires  the  presence  of  an  attendant. 


WORDS,   TERMS  AND  PHRASES. 


55 


4.  By  the  Introduction  of  a  Variable  Resistance  into  the 
shunt  circuit  of  the  machine,  as  in  the  Edison  and  other 
systems. 

This  resistance  may 
be  adjusted  either 
automatically  by  an 
electro- magnet 
whose  coils  are  in  an 
independent  shunt 
across  the  mains,  or 
may  be  operated  by 
hand. 

InFig.35,thevari- 
able  resistance  is 

shown  at  R,  the  lever  switch  being  in  this  case  operated  by 
hand  whenever  the  potential  rises  or  falls  below  the  proper 
value. 

The  machine 
shown  is  thus  en- 
abled to  maintain  a 
constant  potential  on 
the  leads  to  which 
the  lamps,  L  L  L, 
etc.,  are  connected  in 
multiple-arc. 

5.  Dynamometric 
Governing,  in  which 
a  series   dynamo   is 


Fig.  35. 


made  to  yield  a  con- 
stant current  by  gov- 
erning the  steam  engine  that  drives  it,  by  means  of  a  dynamo- 
iiK-tnc  governor  that  maintains  a  constant  torque  or  turning 
moment,  instead    of    the   usual  centrifugal  governor  which 
maintains  a  constant  speed. 
6.  Electric  Governing  of  the  Driving  Engine,  in  which  the 


56 


A  DICTIONARY  OF  ELECTRICAL 


governor  is  regulated  by  the  current  itself  instead  of  by  the 
speed  of  rotation  as  usual. 
(See  Addendum  Automatic  Regulation.) 
Automatic  Telegraphy. — (SeeTelegraphy,  Automatic.) 
Automatic  Telephone  Switch.— (See  Switch,  Tele- 
phone, Automatic.} 

Average  Electro-Motive  Force.— The  mean  value  of 
a  number  of  separate  electro-motive  forces  of  different  values. 
When  a  wire  in  the  armature  of  a  dynamo-electric  machine 
cuts  the  lines  of  magnetic  force  in  the  field  of  the  machine, 
the  electro-motive  forces  produced  depend  on  the  number  of 
lines  of  force  cut  per  second.  This  will  vary  for  different 
positions  of  the  coil.  The  mean  of  the  varying  E.  M.  F.'s 
is  the  average  E.  M.  F. 

Axes  of  Co-Ordiiiates.— (See  Co-Ordinates,  Axes  of.) 
Axis  of  Abscissas. — (See  Abscissas,  Axis  of.) 
Axis  of  Ordinates.— (See  Abscissas,  Axis  of.) 

Axis,     magnetic  of  a 

Straight  Needle.— A  straight  line 
drawn  through  the  magnet,  joining  its 
poles. 

The  magnetic  axis  of  a  straight  needle 
may  be  regarded  as  a  straight  line 
passing  through  the  poles  of  the  needle 
and  its  point  of  support. 

The  magnetic  axis  may  not  corre- 
spond with  the  geometric  axis  of  the 
needle.  This  leads  to  an  error  in  read- 
ing the  true  direction  in  which  the 
needle  is  pointing,  which  must  be  cor- 
rected. Thus,  the  needle  N  S,  Fig.  36, 
points  to  31°  on  the  scale.  In  reality,  if  the  magnetic  axis  of 
the  needle  lies  in  the  line  N'  S',  the  true  deflection  of  the 
needle  is  only  28°. 


My.  36. 


WORDS,  TERMS  AND  PHRASES.  57 

Azimuth. — In  astronomy,  the  angular  distance  between 
an  azimuth  circle  and  the  meridian. 

The  azimuth  of  a  heavenly  body  in  the  Northern  Hemisphere 
is  measured  on  the  arc  of  the  horizon  intercepted  between  the 
north  point  of  the  horizon,  and  the  point  where  the  great  circle 
that  passes  through  the  heavenly  body  cuts  the  horizon. 

Azimuth  Circle.— The  arc  of  a  great  circle  passing 
through  the  point  of  the  heavens  directly  overhead,  called 
the  Zenith,  and  the  point  directly  beneath,  called  the  Nadir. 

Azimuth  Compass. — A  compass  employed  by  navigators 
for  measuring  the  horizontal  distance  of  the  sun  or  a  star  from 
the  magnetic  meridian.  (See  Compass,  Azimuth.) 

Azimuth,  magnetic The  arc  intercepted  on  the 

horizon  between  the  magnetic  meridian  and  a  great  circle 
passing  through  the  observed  body. 

B.  A.  Ohm.— The  British  Association  Unit  of  Resistance, 
adopted  prior  to  1884. 

The  value  of  the  Unit  of  Electric  Resistance,  or  the  ohm, 
was  determined  by  a  Committee  of  the  British  Association 
as  being  equal  to  the  resistance  of  a  column  of  mercury 
at  0°  C.,  one  square  millimetre  in  area  of  cross-section  and 
104.9  centimetres  in  length.  This  length  was  taken  as  com- 
ing nearest  the  value  of  the  true  ohm  deduced  experimentally 
from  certain  theoretical  considerations.  Subsequent  re-deter- 
minations showed  the  value  so  obtained  to  be  erroneous. 
The  value  of  the  ohm  is  now  taken  internationally,  as  adopted 
by  the  International  Electric  Congress  in  1884,  as  the  resistance 
of  a  column  of  mercury  106  centimetres  in  length,  and  one 
square  millimetre  in  area  of  cross-section.  This  last  value  is 
called  the  legal  ohm,  to  distinguish  it  from  the  B.  A.  ohm 
which,  as  above  stated,  is  equal  to  a  mercury  column  104.9 
centimetres  in  length.  Usage  now  sanctions  the  use  of  the 
word  o/tmto  mean  the  legal  ohm. 

This  value  of  the  legal  ohm  is  provisional  until  the  exact 
length  of  the  mercury  column  can  be  finally  determined. 


58  A  DICTIONARY  OF  ELECTRICAL 

The  following  are  the  relative  values  of  these  units,  viz. : 

1  Legal  Ohm =  1.0112  B.  A.  Ohm. 

" =  1.0600  Siemens  Unit 

1  B.  A.  Ohm =    .9889  Legal  Ohm. 

1  B.  A.  Ohm =  1.0483  Siemens  Unit. 

1  Siemens  Unit =    .9540  B.  A.  Ohm. 

" =    .9434  Legal  Ohm. 

Back  Electro-Motive  Force.— A  term  sometimes  used 
for  Counter  Electro-Motive  Force.  The  term  counter  elecl  ro- 
motive  force  is  the  preferable  term.  (See  Counter  Electro- 
Motive  Force.} 

Back  or  Return  Stroke  of  Lightning.— An  elec- 
tric shock,  caused  by  an  induced  charge,  produced  after  the 
discharge  of  a  lightning  flash. 

The  shock  is  not  caused  by  the  lightning  flash  itself,  but  by 
a  charge  which  is  induced  in  neighboring  conductors  by  the 
discharge.  A  similar  effect  may  be  noticed  by  standing  near 
the  conductor  of  a  powerful  electric  machine,  when  shocks 
are  felt  at  every  discharge. 

The  effects  of  the  return  shock  are  sometimes  quite  severe. 
They  are  often  experienced  by  sensitive  people  on  the  occur- 
rence of  a  lightning  discharge  at  a  considerable  distance. 

In  some  instances  the  return  stroke  has  been  sufficiently 
intense  to  cause  death.  In  general,  however,  the  effects  are 
much  less  severe  than  those  of  the  direct  lightning  discharge. 

Balance,  Arms  of (See  Arms  of  Bridge  or  Elec- 
tric Balance.) 

Balance,  Bi-fllar  Suspension An  instrument 

similar  in  its  construction  to  Coulomb's  torsion  balance,  but  in 
which  the  needle  is  hung  by  two  fibres  instead  of  a  single  one. 

Any  deflection  of  the  needle  shortens  the  vertical  distance 
between  the  points  of  support  and  the  needle,  and  so  tends  to 
lift  the  needle.  The  motions  are  therefore  balanced  against 
the  force  of  gravity  instead  of  against  the  torsion  of  the 
fibre. 


WORDS,   TERMS  AND  PHRASES. 


A  bi-filar  suspension  is  shown  in  Fig.  37.  The  two  threads, 
a  6  and  a!  b',  are  connected  to  the  needle  M  N,  so  as  to 
permit  it  to  hang  in  a  true  horizontal 
position.  Any  twisting  around  the  im- 
aginary axis  c  c',  causes  the  lines  of  sus- 
pension, a  b  and  a'  b',  to  tend  to  cross 
one  another  and  so  shorten  the  axis 
c  c'.  M 

Harris,  who  was  the  first  to  employ  *~ 
the  bi-filar  suspension,  showed  that  the  !  , 

reactive  force  imparted  to  the  suspension-  ^    37 

threads  by  turning  the  needle  was  : 

(1)  Directly    proportional    to    the    distance    between    the 
threads. 

(2)  Inversely  as  their  lengths. 

(3)  Directly  proportional  to  the  weight  of  the  suspended  body. 

(4)  As  the  angle  of  twist  or  torsion  of  the  threads  on  each 
other. 

Balance,  Cou- 
lomb's Torsion 

— An  apparatus  to  meas- 
ure the  force  of  electric 
or  magnetic  repulsion  be- 
tween  two  similarly 
charged  bodies,  or  be- 
tween two  similar  mag- 
net poles,  by  opposing  to 
such  force  the  torsion  of 
a  thin  wire. 

The  two  forces  balance 
each  other  ;  hence  the 
origin  of  the  term. 

Fig.    38    represents    a  *  IIL/i- 
Coulomb  torsion  balance 
adapted  to  the  measure- 
ment of  the  force  of  electrostatic  repulsion.     A  delicate  needle 


OF  ELECTRICAL 


of  shellac,  having  a  small  gilded  pith  ball  at  one  of  its  ends, 
is  suspended  by  a  fine  metallic  wire.  A  proof-plane  B  is 
touched  to  the  electrified  surface  whose  charge  is  to  be 
measured,  and  is  then  placed  as  shown  in  the  figure.  (See 
Proof-Plane.)  There  is  a  momentary  attraction  of  the  needle, 
and  then  a  repulsion,  which  causes  the  needle  to  be  moved 
a  certain  distance  from  the  ball  on  the  proof-plane.  This 
distance  is  measured  in  degrees  on  a  graduated  circle  a  a 
marked  on  the  instrument.  The  force  of  the  repulsion 
is  calculated  by  determining  the  amount  of  torsion  required  to 
move  the  needle  a  certain  distance  towards  the  ball  of  the 
electrified  proof-plane. 

This  torsion  is  obtained  by  the  movement  of  the  torsion 
head  D,  the  amount  of  which  motion  is  measured  on  a  gradu- 
ated circle  at  D.  The  measurement  is  based  on  the  fact  that  the 
torsional  force  of  a  wire  is  proportional  to  the  angle  of  torsion. 

Balance,  Hughes'  Induction An  apparatus 

for  the  detection  of  the  presence  of  a  metallic  substance  by 
the  aid  of  induced  electric  currents. 


Two  small  primary  coils  of  wire,  Pj  and  P8,  Fig.  39,  are 
placed  in  the  circuit  of  the  battery  B,  and  microphone  M, 
(See  Microphone.)  Two  small  secondary  coils,  Sj  and  S2,  are 
placed  near  them  in  the  circuit  of  a  telephone,  T.  When  the 
induction  between  Pj  and  S,  is  exactly  equal  to  that  between 


WORDS,   TERMS  AND  PHRASES. 


61 


P2  and  S8  no  sound  is  heard  in  the  telephone,  since  the  cur- 
rents induced  in  Si  and  S8  exactly  neutralize  or  balance  each 
other's  effects. 

If  a  single  coin  or  mass  of  metal  be  introduced  between 
either  St  and  Pt,  or  S2  and  P8,  the  balance  will  be  disturbed 
and  a  sound  will  be  heard,  since  some  of  the  induction  is  now 
expended  in  producing-  electric  currents  in  the  interposed 
metal,  and  a  sound  will  therefore  be  heard  in  the  telephone. 
But  if  precisely  similar  metals  are  placed  in  similar  positions, 
between  St  and  Plt  and  S8  and  P8,  no  sound  is  heard  in  the 
telephone,  since  the  inductive  effects  due  to  the  two  metals 
are  the  same. 

The  slightest  difference,  however,  either  in  composition, 
size,  or  position,  destroys  the  balance,  and  causes  a  sound  to 
be  heard  in  the  telephone. 

A  spurious  coin  is  thus  readily  detected  when  compared 
with  a  genuine  coin. 

A  somewhat  similar  instrument  has  been  employed  to 
detect  and  locate  a  bullet  or  other  foreign  metallic  substance 
in  the  human  body. 

Balance,  Thermic (See  Bolometer,  or  Thermic 

Balance.) 

Balance,    Wheatstone's 

Electric A    device    for 

measuring  the  value  of  electric  re- 
sistances. Q 

A,  B,  C  and  D,  Fig.  40,  are  four 
electric  resistances,  any  one  of 
which  can  be  measured  in  ohms, 
provided  the  absolute  value  of  one 
of  the  others,  and  the  relative  values 
of  any  two  of  the  remaining  three 
are  known  in  ohms. 

A  voltaic  battery,  Zn  C,  is  connected  at  Q  and  P,  so  as 
to  branch  at  P  and  again  unite  at  Q,  after  passing  through 
the  conductor  D  C  and  B  A, 


62  A  DICTIONARY  OF  ELECTRICAL 

A  sensitive  galvanometer,  G,  is  connected  at  M  N,  as 
shown. 

The  passage  of  a  current  through  any  resistance  is  attended 
by  a  fall  of  potential  that  is  proportional  to  the  resistance. 
(See  Potential,  Electric.)  If  then  the  resistances  A,  C  and  B, 
are  so  proportioned  to  the  value  of  the  unknown  resistance 
D,  that  no  current  passes  through  the  galvanometer  G,  the 
two  points,  M  and  N,  in  the  two  circuits,  Q  M  P  and  Q  N  P, 
are  at  the  same  potential.  That  is  to  say,  the  fall  of  poten- 
tial along  Q  M  P  and  Q  N  P,  at  the  points  M  and  N,  is 
equal.  Since  the  fall  of  potential  is  proportional  to  the  resist- 
ance it  follows  that 

A  :  B  :  :  C  :  D, 
or  A  X  D  =  B  X  C, 

orD=(l)c- 

If  then  we  know  the  values  of  A,  B  and  C,  the  value  of  D 
can  be  readily  calculated. 
B 
By  making  the  value  —  some  simple  ratio,  the  value  of  D  is 

easily  obtained  in  terms  of  C. 

The  resistances  A,  B  and  C,  may  consist  of  coils  of  wire 
whose  resistance  is  known.  To  avoid  their  magnetism  affect- 
ing the  needle  during  the  passage  of  the  current  through  them, 
they  should  be  made  of  wire  bent  into  two  parallel  wires 
and  wrapped  in  coils  called  resistance  coils,  or  a  resistance-box 
may  be  used.  (See  Coils,  Resistance.  Box,  Resistance.) 

There  are  two  general  forms  of  Wheatstone's  Balance,  viz. : 
the  box  forni;  and  the  sliding  form. 

Balance,  Wheatstone's  Electric ,  Box  or 

Commercial  Form  of  Wheatstone's  Bridge.— A 
commercial  form  of  bridge  or  balance  in  which  all  three  known 
arms  or  branches  of  the  bridge  consist  of  standardized  resist- 


WORDS,    TERMS   AND  PHRASES. 


ance  coils,    whose  values    are   given  in  ohms.     (See  Coils, 

Resistance.) 

The  box  form  of 
bridge  is  shown  in 
perspective  in  Fig. 
41,  and  in  plan  in 
Fig.  42.  The  bridge 
arms,  correspond- 
ing to  the  resist- 
!  ances  A  and  B,  of 
Fig.  40,  consist  of 
resistance  coils  of 
10,  100,  and  1,000 


ohms  each,  insert- 
ed in  the  arms  qz, 
and  q  x,  of  Fig. 
42.    (See  Balance,  /•- 
Wheatstone's  D 
Electric.)     These 
are  called  the  pro- 
portional  coils. 
The    arm    corre- 
sponding to  resist- 


Mg.  43. 
induction,  among-  wl 


Fig.  It2. 

ance  C,  of  Fig.  40,  is  composed 
of  separate  resistances  of  1,  2, 
2,  5, 10,  10,  20,  50,  100,  100, 200 
500,  1,000,  1,000,  2,000,  and 
5,000  ohms.  In  some  forms 
of  box  bridges,  additional 
decimal  resistances  are  added. 
The  resistance  coils  are 
wound,  as  shown  in  Fig.  43, 
after  the  wire  has  been  bent 
on  itself  in  the  middle,  in 
order  to  avoid  the  effects  of 
ich  are  a,  disturbing  action  on  a  galvano 


(54 


A  DICTIONARY  OF  ELECTRICAL 


meter  used  near  them,  and  the  introduction  of  a  spurious 
resistance  in  the  coils  themselves.  (See  Spurious  Resistance.) 
To  avoid  the  effects  of  changes  of  resistance  occasioned  by 
changes  of  temperature,  the  coils  are  made  of  German  silver, 
or  preferably  of  alloys  called  Platinoid,  or  Platinum  silver. 
(See  Platinoid.  Platinum  Silver.)  Even  when  these  alloys  are 
used,  care  should  be  taken  not  to  allow  the  currents  used  to 
pass  through  the  resistance  coils  but  for  a  few  moments. 

The  coils,  C  C',  are  connected  with  one  another  in  series  by 
connecting  their  ends  to  the  short,  thick  pieces  of  brass,  E  E  E, 
Fig.  43.  On  the  insertion  of  the  plug  keys,  at  S  S,  the  coils  are 
cut  out  by  short-circuiting.  Care  should  be  taken  to  see  that 
the  plug  keys  are  firmly  inserted  and  free  from  grease  or  dirt, 
otherwise  the  coil  will  not  be  completely  cut  out. 

The  following  are  the  connec- 
tions, viz. :  The  galvanometer  is 
inserted  between  q  and  r,  Fig. 
44;  the  unknown  resistance  be- 
tween z  and  r  ;  the  battery  is 
connected  to  x  and  z.  A  con- 
venient proportion  being  taken 
for  the  value  of  the  proportional 
coils,  resistances  are  inserted  in 
C,  until  no  deflection  is  shown  by 
the  galvanometer  G.  The  simi- 
larity between  these  connections  and  those  shown  in  Fig.  42. 
will  be  seen  from  an  inspection  of  Fig.  44.  (See  Balance, 
Wheatstone's  Electric.)  The  arms,  A  and  B,  correspond  to 
q  x  and  q  z,  of  Fig.  42  ;  C,  to  the  arm  x  r,  Fig.  42  ;  and  D,  to 
the  unknown  resistance.  We  then  have  as  before 

/  B  \ 
A  :  B  :  :  C  :  D.,  or  A  X  D  =  B  X  C, .-.  D  =  I  —  J    C. 

The  advantage  of  the  simplicity  of  the  ratios,  A  and  B,  or 
10,  100,  and  1,000,  of  the  Bridge  Box,  will  therefore  be  mani- 


WORDS,   TERMS  AND  PHRASES.  65 

fest.  The  battery  terminals  may  also  be  connected  to  q  and  r, 
and  Ibo  galvanometer  terminals  to  x  and  z,  without  disturb- 
ing the  proportions. 


Flg.tti, 
Balance,  Whcatstoiic's,  Slide  Form  of A 


66  A  DICTIONARY   OF  ELECTRICAL 

balance  in  which  the  proportionate  arms  of  the  bridge  are 
formed  of  a  single  thin  wire,  of  uniform  diameter,  generally  of 
German  silver^  of  comparatively  high  resistance. 

A  Spring  Key  slides  over  the  wire  ;  one  terminal  of  the  key 
is  connected  with  the  galvanometer  and  the  other  with  the 


,W 


Fig.  IS. 

wire  when  the  spring  key  is  depressed.  As  the  wire  is  of 
uniform  diameter,  the  resistances  of  the  arms,  A  and  B,  Fig. 
46,  will  then  be  directly  proportional  to  the  lengths.  A  scale 
placed  near  the  wire  serves  to  measure  these  lengths.  A 
thick  metal  strip  connected  to  the  slide  wire  has  four  gaps  at 
P,  Q,  R  and  S. 

When  in  ordinary  use,  the  gaps  at  P  and  S  are  either  con- 
nected by  stout  strips  of  conducting  material  or  by  known 
resistances,  in  which  case  they  act  simply  as  ungradu:i1f<l 
extensions  of  the  slide  wire,  and,  like  lengthening  the  slide 
wire,  increase  the  sensibility  of  the  instrument. 

The  unknown  resistance  is  then  inserted  in  the  gap  at  Q, 
and  a  known  resistance,  generally  the  resistance  box,  in  that 
at  R.  The  galvanometer  has  one  of  its  terminals  connected 
to  the  metal  strip  between  Q  and  R,  and  its  other  terminal  to 
the  sliding  key.  The  battery  terminals  are  connected  to  the 
metal  strips  between  P  and  Q,  and  R  and  S,  respectively. 

These  connections  are  more  clearly  seen  in  the  form  of 
bridge  shown  in  Fig.  45.  The  slide  wire  w  w,  consists  of  three 
separate  wires  each  a  metre  in  length,  so  arranged  that  only 
one  wire,  or  two  in  series,  or  all  three  in  series,  can  be  used. 
Matters  being  now  arranged  as  shown,  the  sliding  key  is 
moved  until  no  current  passes  through  the  galvanometer. 


\\o|;|>s.    TI'.KMS    AND  PHRASES. 


07 


The  sliding  bridge  is  not  entirely  satisfactory,  since  the 
uncertainty  of  Hie  spring-contact  causes  a  lack  of  correspond- 
ence between  the  point  of  contact  and  Hie  point  of  the  scale 
on  which  the  index  rests. 

The  loss  of  uniformity  of  the  wire,  due  to  constant  use, 
causes  a  lack  of  correspondence  between  the  resistance  of  Hie 
wire  and  its  length.  With  cai-e,  however,  very  accurate  re- 
sults can  be  obtained. 

Ballistic  Curve. — The  curve  actually  described  by  a  pro- 
jectile thrown  in  any  other  than  a  vertical  direction  through 
the  air. 

Theoretically,  the  path  of  a  pro- 
jectile in  a  vacuum  is  a  parabola 
—that  is,  the  path  A  E  B,  Fig.  47. 
Actually,  the  effects  of  fluid  resist- 
ances cause  it  to  take  the  path  A 
C  D,  called  a  ballistic  curve.  The 
ballistic  curve  has  a  smaller  verti- 
cal height  than  the  parabola.  The 
projectile  also  has  a  smaller  vertical  range.  Instead  of  reach- 
in-  the  point  B,  it  continually  approaches  the  perpendicular 
EF. 

Ballistic  Galvanometer.— A  form  of  galvanometer 
suitable  for  measuring  momentary  currents,  such  as  those 
produced  by  the  discharge  of  a  condenser,  which  rise  rapidly 
from  zero  to  a  maximum,  and  then  as  rapidly  fall  to  zero. 
(See  Galvanometer,  Ballistic.) 

Bnrsul.— A  unit  of  pressure  recently  proposed  by  the  Brit- 
ish Association. 

One  barad  equals  one  dyne  per  square  centimetre. 

Barometer. — An  apparatus  for  measuring  the  pressure 
of  the  atmosphere. 

Barometric  Column.— A  column,  usually  of  mercury, 
approximately  thirty  indies  in  vertical  height,  sustained  in 
a  barometer  or  other  tube  by  the  pressure  of  the  atmosphere. 


A  DICTIONARY   OF  ELECTRICAL 


The  space  above  the  bai-ometric  column  contains  a  vacuum 
known  as  the  Torricellian  vacuum. 

Bars,  Krizik's Cores  of  various  shapes,  provided 

for  solenoids,  in  which  the  distribution  of  the  metal  in  the  bar 
is  so  proportioned  as  to  obtain  as  nearly  as  possible  a  uniform 
attraction  or  pull  while  in  different  positions  in  the  solenoid. 

Various  Krizik's 
bars  are  shown  in 
Fig.  48.  As  will  be 
observed,  in  all 
cases  the  mass  of 
metal  is  greater 
towards  the  middle 
of  the  bar  or  core 
than  near  the  ends. 
When  a  core  of 
uniform  diameter  is 
drawn  into  a  sole- 
noid, the  attraction  or  pull  is  not  uniform  in  strength  for  dif- 
ferent positions  of  the  bar.  When  the  bar  is  just  entering  the 
Kolenoid,  the  pull  is  the  strongest ;  as  soon  as  the  end  passes 
the  middle  of  the  core  the  attraction  grows  less,  until,  when 
the  centres  of  the  bar  and  core  coincide,  the  motion  ceases, 
since  both  ends  of  the  solenoid  attract  equally  in  opposite 
directions.  By  proportioning  the  bars,  as  shown  in  the  figure, 
a  fairly  uniform  pull  for  a  considerable  length  may  be  ob- 
tained. 

Bath,  Electro-Therapeutic A  bath  furnished 

with  suitable  electrodes  and  used  in  the  application  of  elec- 
tricity to  curative  purposes.  Such  baths  should  be  used  only 
under  the  advice  of  an  intelligent  physician. 

Bath,  Electro-Plating Tanks  containing  me- 
tallic solutions  in  which  articles  are  placed  that  are  to  be 
electro-plated.     (See  Electro-Plating.} 
Bathometer.— An  instrument  invented  by  Siemens  for 


WORDS,    TERMS  AND  PHRASES.  69 

obtaining  deep-sea  soundings  without  the  use  of  a  sounding 
Hne. 

The  bathometer  depends  for  its  operation  on  the  decreased 
attraction  of  the  earth  for  a  suspended  weight,  that  takes  place 
in  parts  of  the  ocean  differing  in  depth.  As  the  vessel  passes 
over  deep  portions  of  the  ocean,  the  solid  land  of  the  bottom, 
being  further  from  the  ship,  exerts  a  smaller  attraction  than 
it  would  in  shallow  parts,  where  it  is  nearer  ;  for,  although  in 
the  deep  parts  of  the  ocean  the  water  lies  between  the  ship 
and  the  bottom,  the  smaller  density  of  the  water  as  compared 
with  the  land  causes  it  to  exert  a  smaller  attraction  than  in 
the  shallower  parts,  where  the  bottom  is  nearer  the  ship.  The 
varying  attraction  is  caused  to  act  on  a  mercury  column,  the 
reading  of  which  is  effected  by  means  of  an  electric  contact. 

Batlis,  Copper,  Gold,  Silver,  Nickel,  etc., 

Tanks  containing  solutions  of  metals  suitable  for  electric 
deposition  by  the  process  of  electro-plating.  (See  Electro- 
Plating.) 

Batlerie§,  Varieties    of  Voltaic (See  Cell, 

Voltaic,  Varieties  of.) 

Battery,  Dynamo  —  —The  combination  or  coup- 
ling together  of  several  separate  dynamo-electric  machines  so 
as  to  act  as  a  single  electric  source. 

The  dynamos  may  be  connected  to  the  leads  either  in  series, 
in  multiple-arc,  in  multiple-series,  or  in  series-multiple. 

Battery,  Electric A   general  term  applied  to 

the  combination,  as  a  single  source,  of  a  number  of  separate 
electric  sources. 

The  separate  sources  may  be  coupled  either  in  series,  in 
multiple-arc,  in  multiple-series,  or  in  series-multiple.  (See  Cir- 
cuits, Varieties  of.) 

The  term  battery  js  sometimes  incorrectly  applied  to  a  single 
voltaic  couple  or  cell. 

Battery,  L,cy«lcii  Jar —  —The  combination  of  a 
number  of  separate  Leydeu  jars  so  as  to  act  as  one  single  jar. 


70 


A   DICTIONARY  OF  ELECTRICAL 


A  Leyden  battery  is  shown  in  Fig.  49,  where  nine  separate 
Leyden  jars  are  connected  as  a  single  jar  by  joining  their 
outer  coatings  by  placing  them  in  the  box  P,  the  bottom  of 


Fig.  49. 

which  is  lined  with  tin  foil.  The  inner  coatings  are  con- 
nected together  by  the  metal  rods  B,  as  shown. 

A  discharging  rod  A'  may  be  employed  for  connecting  the 
opposite  coatings.  The  handles  arc  made  of  glass  or  any 
good  insulating  material. 

Buttery,  I  .oral A  voltaic  battery  used  at  either 

end  of  a  telegraph  line  to  operate  the  Morse  sounder,  or  the 
registering  or  recording  apparatus,  at  that  end  only.  (See 
Telegraphy,  Morse  System  of.) 

The  local  battery  is  tin-own  into  or  out  of  action  by  the 
telegraphic  relay.  (See  Relay. ) 


WORDS,   TERMS   AND   PHRASES. 


71 


Battery,  Magnetic 


— The  combination,  as  a  single 


magnet,  of  a  number  of  separate  magnets. 

A  magnetic  battery,  or  compound  magnet, 
is  shown  in  Fig.  50.  It  consists  of  straight 
bars  of  steel,  p  p  p,  with  their  similar  poles 
placed  near  together,  and  inserted  in  masses 
of  soft  iron,  N  and  S,  as  shown. 

Battery.,  Plunge —A  number  of 

voltaic  cells  connected  so  as  to  form  a  single 
cell  or  electric  source,  the  plates  of  which 
are  so  supported  on  a  horizontal  bar  as 
to  be  capable  of  being  simultaneously 
placed  in,  or  removed  from,  the  liquid. 

The  plunge  battery  shown  in  Fig1.  51  con- 
sists of  a  number  of  zinc-carbon  elements 
immersed  in  an  electrolyte  of  dilute  sul- 
phuric acid,  or  in  electropoion  liquid,  con- 


Fig.  M. 


tained  in  separate  jars,  J,  J.     (See  Electropoion  Liquid.) 


Battery,  Primary —  —The  combination  of  a  num- 
ber of  primary  cells  so  as  to  form  a  single  source. 

The  term  jtriiniiri/  litiffer//  is  used  in  order  to  distinguish  it 
from  secondary  or  storage  battery.  (See  Storage  Cells  or  Accu- 
mulators.) 


72  A  DICTIONARY  OF  ELECTRICAL 

Battery,  Secondary The  combination  of  a 

number  of  secondary  or  storage  cells  so  as  to  form  a  single 
electric  source.  (See  Storage  of  Electricity.) 

Battery,  Selenium The  combination  of  sele- 
nium with  another  element  to  form  an  electric  source  when 
acted  on  by  light. 

Battery,  Split A  voltaic  battery  connected  in 

series,  and  having  one  of  its  middle  plates  connected  with 
the  ground. 

By  this  means  the  poles  of  a  battery  are  maintained  at 
potentials  differing  in  opposite  directions  from  the  potential 
of  the  earth. 

Battery,  Thermo-Electric The  combination, 

as  a  single  thermo-electric  cell,  of  a  number  of  separate  thermo- 
electric cells  or  couples.  (See  Thermo-Electric  Couple.) 

Battery,  Voltaic,  Closed-Circuit A  voltaic 

battery  which  may  be  kept  constantly  on  closed  circuit. 

The  gravity  battery  is  a  closed-circuit  battery.  As  em- 
ployed for  use  on  most  telegraph  lines,  it  is  maintained  on 
a  closed  circuit.  When  an  operator  wishes  to  use  the*line  lie 
opens  his  switch,  thus  breaking  the  circuit  and  calling  his 
correspondent.  Such  batteries  should  not  polarize.  (See 
Polarization  of  Voltaic  Cell.) 

Battery,  Voltaic,  Open-Circuit  —A  voltaic 

battery  which  is  normally  on  open-circuit,  and  which  is  used 
for  comparatively  small  durations  of  time  on  closed  circuit. 

The  Leclanche-cell  is  an  excellent  open-circuited  battery. 
It  has  a  comparatively  high  electro-motive  force,  but  rapidly 
polarizes.  It  cannot  therefore  be  economically  used  for 
furnishing  currents  continuously  for  long  durations  of  time. 
When  left  on  open  circuit,  however,  it  depolarizes.  (See  Cell, 
Voltaic,  Leclanche.) 

Battery,  Voltaic The  combination,  as  a  single 

source,  of  a  number  of  separate  voltaic  cells. 

Battery,  Water  —  —A  battery  formed  of  zinc  and 
copper  couples  immersed  in  ordinary  water. 


WORDS,    TERMS  AND  PHRASES.  73 

Any  voltaic  couple  cr.n  be  used,  the  positive  element  of 
which  is  capable  of  being  slightly  acted  on  by  water.  When 
numerous  couples  are  employed  considerable  difference  of 
potential  can  be  obtained. 

Water  batteries  are  employed  for  charging  electrometers. 
They  are  not  capable  of  giving  any  considerable  current, 
owing  to  their  great  internal  resistance. 

B.  A.  U. — A  contraction  sometimes  employed  for  the  Brit- 
ish Association  Unit  or  Ohm. 

Bell  €all,  Electric An  electric  bell  used  to  call 

the  attention  of  an  operator  to  the  fact  that  his  correspondent 
wishes  to  communicate  with  him. 

Bell,  Extension  Call  — A  device  for  prolonging 

the  sound  of  a  magneto  call,  and  for  sounding  the  signal  at 
some  distant  point. 

An  alarm-bell  is  connected  with  the  circuit  of  a  local  bat- 
tery by  the  current  generated  by  the  magneto  call,  and  con- 
tinues sounding  after  the  current  of  the  magneto  call  has 
ceased. 

Bell,  Indicating; An  electric  bell  in  which,  in 

order  to  distinguish  between  a  number  of  bells  in  the  same 
office,  a  number  is  displayed  by  each  bell  when  it  rings. 

Bell  Magnet— (See  Magnet,  Bell.) 

Bell,  Magneto  Call Telephone  Call 

A  call-bell  operated  by  currents  generated  by  the  rotation  of 
an  armature  in  a  magnetic  field. 

Bell*,  Relay -—Bells  used  in  the  early  forms  of 

of  acoustic  telegraphs  as  employed  in  England  with  relay 
sounders. 

The  dots  and  dashes  of  the  Morse  alphabet  were  indicated 
by  the  sounds  of  a  bell,  a  tap  on  one  bell  indicating  a  dot,  and 
a  tap  on  the  other  a  dash.  This  system  is  now  practically 
abandoned. 

Bias  of  Relay  Tongue,— A  terra  to  signify  the  adjust- 


74 


A  DICTIONARY  OF   ELECTRICAL 


ment  of  a  polarized  relay  such  that,  on  the  cessation  of  the 
working  current,  the  relay  tongue  shall  always  rest  against 
the  insulated  contact  and  not  against  the  other  contact,  or 
vice  versa. 

Sometimes,  as  in  the  split-battery-duplex,  the  bias  is  toward 
the  uninsulated  contact.  (See  Relay,  Polarized.) 

Bichromate  Voltaic  Cell.— (See  Cell,  Voltaic.) 

Bi-Filar  Balance.— (See  Balance,  Bi-fllar  Suspension.) 

Bi-Filar  Suspension.— The  suspension  of  a  needle  or 
magnet  by  two  fibres  in  place  of  a  single  fibre.  (See  Bal- 
ance, Bi-Filar  Suspension.) 

Bi-Filar  Winding  of  Coils.— A  winding  of  a  coil  of 
wire  such  that,  instead  of  winding  it  in  one  continuous  length, 
the  wire  is  doubled  in  itself  and  then  wound. 

This  method  is  employed  in  resistance  coils,  so  as  to  avoid 
disturbing  effects  on  neighboring  instruments.  (See  Coils, 
Resistance.) 

Binary  Compound.— In  chemistry,  a  compound  formed 
by  the  union  of  two  different  elements. 

Water  is  a  binary  compound,  being  formed  by  the  union 
of  two  atoms  of  hydrogen  with  one  atom  of  oxygen.  Its 
chemical  composition  is  thus  expressed  in  chemical  symbols, 
viz.,  H8O,  which  indicates  two  atoms  of  hydrogen  combined, 
or  chemically  united,  with  one  atom  of  oxygen. 
I' 


Binding  Posts,  or  Binding  Screws.— Devices  for 
connecting  the  terminals  of  an  electric  source  with  those  of  an 


WORDS,   TERMS  AND  PHRASES.  75 

electro-receptive  device,  or  for  connecting-  different  parts  of  an 
electric  apparatus  with  one  another. 

The  conducting  or  circuit  wire  is  either  introduced  in  the 
opening-  a,  Fig.  52,  and  clamped  by  the  screw  b  ;  or  is  placed 
in  the  space,  dd,  and  kept  in  place  by  means  of  a  thumb-screw, 
Sometimes  two  openings  are  provided  at  c  and  c',  for  the 
purpose  of  connecting  two  wires  together. 

Biology,  Electro (See  Electro-Biology.) 

Black  Lca<l. — A  variety  of  carbon  employed  in  various 
electrical  processes. 

Black  lead  is  also  termed  plumbago  or  graphite.  (See  Plum- 
bago. Graphite.) 

Blasting,  Electric The  electric  ignition  of  pow- 
der or  other  material  in  a  blast.  (See  Fuse,  Electric.) 

Bleaching,  Electric Bleaching  processes  in 

which  the  bleaching  agents  are  liberated  as  required  by 
the  agency  of  electrolytic  decomposition. 

In  the  process  of  Naudin  and  Bidet,  the  current  from  a  dy- 
namo-electric machine,  is  passed  through  a  solution  of  common 
salt  between  two  closely  approached  electrodes.  The  chlorine 
and  sodium  thus  liberated  react  on  each  other  and  form  so- 
dium byphochloride,  which  is  drawn  off  by  means  of  a  pump 
and  used  for  bleaching.  (See  Electrolysis.) 

Block,  Branch (See  Branch  Block.) 

Block  System  for  Rail  ways.— A  system  for  securing 
safety  from  collisions  of  moving  railroad  trains  by  dividing 
the  road  into  a  number  of  blocks  or  sections  of  a  given  length, 
and  so  maintaining  telegraphic  communication  between 
lowers  located  at  Hie  endsof  each  of  such  blocks,  as  to  prevent, 
l.y  Hie  display  of  suitable  signals,  more  than  one  train  or  en- 
gine from  being  on  the  same  block  at  the  same  time. 

There  are  two  kinds  of  block  railway  systems,  viz.  : 

(1)  The  Absolute  ///»<•/,•  fii/xtrm. 

(2)  The  Pcnuissin:  I  Hock  Xt/stem, 


76  A  DICTIONARY  OF  ELECTRICAL 

In  the  absolute  system,  which  is  of  course  the  safest,  one 
train  only  is  permitted  to  be  on  any  particular  block  at  a 
given  time. 

In  the  permissive  block  system  more  than  one  train  is  per- 
mitted, under  certain  circumstance  and  conditions,  to  occupy 
the  same  block  simultaneously,  each  train  then  being  notified 
of  the  fact  that  it  is  not  alone  on  the  block. 

The  absolute  block  system,  though  expensive  to  construct 
arid  maintain,  is  the  only  one  that  should  be  permitted  in  law 
to  exist  on  roads  whose  traffic  reaches  a  certain  amount. 

The  absolute.block  system  is  employed  on  the  London  Un- 
derground Railroad,  and  on  the  Pennsylvania  Railroad 
Systems. 

The  system,  as  in  use  on  the  New  York  division  of  the 
Pennsylvania  Railroad,  is  as  follows  : 


The  road  between  Philadelphia  and  Jersey  City  is  divided 
into  some  seventy  sections,  the  length  of  each  section  being 
dependent  on  the  amount  of  daily  traffic  ;  thus,  between 
Jersey  City  and  Newark,  where  the  traffic  is  great,  there  are 


WORDS,   TERMS  AND  PHRASES.  77 

some  fifteen  sections,  although     the    distance  is  only    7.9 
miles. 

In  each  block-tower  there  are  connections  with  three  separ- 
ate and  distinct  telegraph  lines  or  circuits,  viz.  : 

(1)  A  line  or  wire  called  the  train  wire,  connecting  the 
block-tower  with   the  Genei'al  Dispatcher's  office  at  Jersey 
City.     This  line  is  used  for  sending  train  orders  only. 

(2)  A  line  or  wire  called  the  block  wire,  connecting  each 
block-tower  with  the  next  tower  on  each  side  of  it. 

(3)  A  line  or  wire  called  the  message  wire,  and  used  for  local 
traffic  or  business. 

The  general  arrangement  of  the  block-tower  is  shown  in 
Fig.  53. 

Each  of  the  block-towers  is  sufficiently  elevated  above  the 
road-bed  to  afford  the  operator  an  unobstructed  view  of  the 
tracks. 

The  operator,  having  ascertained  the  actual  condition  of  the 
track  either  by  observation,  or  by  telegraphic  communica- 
tion with  the  stations  on  either  side  of  him,  gives  notice  of 
this  condition  to  all  trains  passing  his  station  by  the  display 
of  certain  semaphore  signals. 

The  semaphore  signals  as  used  on  this  road  are  shown  on 
following  pages,  in  Figs,  54  and  55.  The  form  shown  in  Fig. 
54  is  used  in  the  absolute  system,  and  that  shown  in  Fig.  55  in 
the  permissive  system.  These  signals  consist  essential!}'  of 
an  upright  support  provided  with  a  movable  arm  A  B,  called 
the  semaphore  arm,  capable  of  being  set  in  any  of  two,  or  three 
positions.  The  semaphore  signal  is  placed  outside  the 
signal  tower,  often  several  hundred  feet  away,  but  is 
readily  set  from  the  tower  in  any  of  the  desired  positions  by 
the  operator,  by  the  movement  of  rods  connected  with  levers. 

The  semaphore  arm  can,  in  the  permissive  system,  be  set  in 
three  positions,  viz. : 

(1)  In  a  horizontal  position,  or  where  the  semaphore  arm 
makes  an  angle  of  90°  with  the  upright. 


•ft*  A  DICTIONARY  OF  ELECTRICAL 

(2)  Or  it  may  be  dropped  down  from  the  horizontal  position 
through  an  angle  of  75°,  as  shown  in  Fig.  54. 

(3)  Or  it  may  occupy  a  position  exactly  intermediate  be- 


kj~ 


tween  the  first  and  the  second,  or  37°  30'  below  the  horizontal, 
as  shown  in  Fig.  55. 


WORDS,    TERMS  AND  PHRASES.  79 

Position  No.  1,  is  the  danger  signal,  and  when  it  is  displayed 
ihe  train  niajr  not  enter  the  block  it  governs. 


Position  No.  2  shows  that  the  track  is  clear,  and  that  the 
train  may  safely  enter  the  block  it  governs. 
Position  No.  3,  which  is  used  in  the  permissive  block  system 


80  A  DICTIONARY  OF  ELECTRICAL 

only  signifies  caution,  and  permits  the  train  to  cautiously 
enter  the  block  and  look  out  for  further  signals. 

The  semaphore  arm  consists  of  a  light  wooden  arm,  11 
inches  wide  hy  5)£  feet  in  length,  painted  red,  or  other 
suitable  color  that  can  be  easily  distinguished  by  daylight. 

By  night  the  positions  of  the  semaphore  arm  are  indicated 
by  colored  lights.  These  lights  are  operated  as  follows  ;  viz., 
in  the  absolute  system,  the  semaphore  arm  A  B,  pivoted  at 
A,  bears  at  its  shorter  end  a  disc  or  lens  of  red  glass  R,  and, 
in  the  permissive  system,  below  this  another  disc  or  lens  of 
green  glass  G.  An  oil  lantern,  provided  with  an  uncolored 
glass  lens,  is  so*  supported  on  a  bracket  fastened  to  the  up- 
right that  when  the  semaphore  arm  points  to  danger,  the  red 
glass  is  immediately  in  front  of  the  lantern  ;  when  it  points  to 
caution,  the  green  glass  is  in  front  of  the  lantern ;  but 
when  it  points  to  safety,  the  lantern  is  left  uncovered  save 
by  its  uncolored  glass. 

At  night,  therefore,  when  the  semaphore  arm  is  set  to 
danger,  a  red  light  is  displayed  ;  when  it  points  to  caution,  a 
green  light  is  displayed  ;  and  when  it  points  to  safely,  a  white 
light  is  displayed. 

The  green  light  is  only  used  in  the  permissive  block  system. 
In  the  absolute  block  system,  'the  semaphore  arm  has  two 
positions  only  ;  viz.,  danger,  or  horizontal,  and  safety,  or  75° 
below  the  horizontal. 

A  single  arm  is  used  when  it  is  intended  to  govern  a  single 
track  only.  Where  the  condition  of  a  number  of  tracks  is  to 
be  indicated,  several  arms  are  employed,  one  above  the  other. 

When  semaphore  signals  are  placed  on  each  side  of  a  double- 
track  road,  the  semaphore  arm  pointing  to  the  right  of  the 
vertical  support  governs  the  line  running  to  the  right. 

When  the- semaphore  signals  are  placed  at  junctions  or 
switch-crossings,  the  operator  in  the  signal-tower  opens  or 
closes  the  switches  from  the  tower  by  the  movements  of 
levers  that  set  the  switches,  and  then  displays  the  proper 


WORDS,   TERMS  AND   PHRASES.  81 

semaphore  signal  for  that  crossing  or  route,  red,  or  danger,  if 
the  route  is  blocked,  and  white,  or  safety,  if  it  is  clear.  Here 
the  interlocking  apparatus  is  employed,  which  consists  in  a 
device  by  means  of  which,  when  a  route  has  once  been  set  up 
and  a  signal  given  for  that  poute,  the  switches  and  signals  are 
so  interlocked  that  no  signal  can  possibly  be  given  for  a  con- 
flicting route. 

The  signals  or  switches  are  operated  by  means  of  iron  rods 
passing  over  rollers  or  pulleys.  These  rods  are  attached  by 
suitable  connections  to  the  switch  or  semaphore  signals,  and 
are  operated  by  means  of  levers  from  the  signal -tower. 
Switches  can  be  operated  as  far  as  1,000  feet  from  the  tower  ; 
signals  as  far  as  2,500  feet. 

Colored  switch-signals  are  placed  opposite  the  end  of  the 
switches  to  indicate  the  positions  of  the  switch.  These  sig- 
nals consist  of  red  and  white  discs  for  day,  and  a  lantern  pro- 
vided with  red  and  white  glasses  for  night.  When  the  switch 
on  any  line  is  open,  the  switch-signal  shows  red ;  when  shut, 
it  shows  white.  These  switch-signals  are  only  used  in  the 
yards. 

No  passenger  train  is  permitted  on  a  block,  after  another 
train  has  passed  the  signal  station,  until  a  dispatch  has  been 
received  from  the  station  ahead  that  the  train  has  passed  and 
the  block  is  thus  cleared. 

As  an  additional  precaution  against  rear  collisions,  tail- 
lights  are  displayed  at  the  ends  of  the  trains.  These  consist 
of  lanterns  placed  on  each  side  of  the  rear  end  of  the  last 
car.  These  lanterns  are  furnished  with  three  glass  slides. 
The  side  of  the  lantern  towards  the  rear  of  the  car  shows  a 
red  light ;  that  to  the  front  and  side  of  the  car  shows  a  green 
light.  The  engineer,  looking  out  of  the  cab,  can  thus  see  a 
green  light,  which  serves  as  a  "  marker"  and  indicates  to  him 
that  his  train  is  intact.  By  day  a  green  flag,  placed  in  the 
same  position  as  the  lantern,  serves  the  same  purpose  as  a 
marker.  An  observer  on  the  track,  or  in  the  tower,  sees  the 
red  lights  on  the  rear  of  the  train  when  it  has  passed. 


A   DICTIONARY  OF  ELECTRICAL 


Freight  trains  are  now  run  on  separate  tracks,  except 
in  places  where  the  extra  tracks  are  not  yet  completed. 
Here  they  do  not  run  on  schedule  time,  but  are  permitted  to 
follow  one  another  at  intervals  that  depend  on  the  condition 
of  the  tracks  as  shown  by  the  signals  displayed. 

Blow-Pipe,  Electric A  blow-pipe  in  which  the 

p  P  air-blast  is  supplied 

by  the  stream  of  air 
particles  produced 
at  the  point  of  a 
chai-ged  conductor 
by  the  convection 
discharge. 

The  candle  flame 
Fig.  56,  is  blown 
in  the  direction 
shown  by  the  stream 
of  air  particles  pass- 
ing off  from  the  point  P.  (See  Convection,  Electric.) 

Blow-Pipe,  Electric  Arc A  device  of  Wer- 

dermann  for  cutting  rocks,  or  other  refractory  substances,  in 
which  the  heat  of  the  voltaic  arc  is  directed  by  means  of  a 
magnet,  or  blast  of  air,  against  the  substance  to  be  cut. 

The  carbons  are  placed  parallel,  so 
as  to  readily  enter  the  cavity  thus  cut 
or  fused.  This  invention  has  never 
been  introduced  into  extensive  prac- 
tice. 

As  shown  in  Fig.  57  the  voltaic  arc, 
taken  between  two  vertical  carbon  elec- 
trodes, is  deflected  into  a  horizontal  posi- 
tion under  the  influence  of  the  inclined 
poles  of  a  powerful  electro-magnet. 

The  highly  heated  carbon  vapor  that  -^  57- 

constitutes  the  voltaic  arc   is  deflected  by  the   magnet  in 


WORDS,   TERMS  AND  PHRASES.  83 

the   same  direction  as  would  be  any  other  movable  circuit  or 
current. 

Board,  Multiple  SwilHi  —  —Aboard  to  which  the 
numerous  circuits  employed  in  systems  of  telegraphy,  tele- 
phony, annunciator,  or  electric  light  and  power  circuits,  are 
connected. 

Various  devices  are  employed  for  closing  these  circuits,  or 
for  connecting,  or  cross-connecting,  them  with  one  another, 
or  with  neighboring  circuits. 

A  multiple  switch  board,  for  example,  for  a  telephone 
exchange,  will  enable  the  operator  to  connect  any  subscriber 
on  the  line  with  any  other  subscriber  on  that  line,  or  on 
another  neighboring  line  provided  with  a  multiple  switch- 
board. To  this  end  the  following  parts  are  necessary  : 

(1)  Devices  whereby  each  line  entering  the 
exchange  can  readily  have  inserted  in  its  circuit 
a  loop  connecting  it  with  another  line.     This 
is   accomplished  by   placing    on    the    switch- 
board  a  separate  *i>rin<i-jtn-k  connection   for 
•  •at -h   separate  line.     Tins  connection  consists 
essentially  of  one  or  Iwo  springs  made  of  any 
conducting  metal,  which  are  kept  in  metallic 
contact  but  which  can  be  separated  from  one 
another  by  the  introduction  of  the  ping  key, 
terminals,  a  and  b,  of  which  are  insulated  from  each  other,  ami 
are  connected  to  the  ends  of  a  loop  coming  from  another  line. 
As  the  key  is  inserted,  the  metallic  spring  or  springs  of  the 
spring-jack  arc  separated,  and  the  metallic  pieces,  a  and  b, 
brought  inlo  good  sliding  contact  therewith,  thus  introducing 
the  !.»>p  into  the  circuit.     (See  Spring-Jci( •/.-.) 

(2)  As  many  separate  Annunciator  Drops  as  there  areseparate 
subscribers.     These  are  provided  so  as  to  notify  the  Central 
'Mliceol'the   p;irticular  subscriber  who  desires  a  connection. 
Alarm-bells,  to  call  the  operator's  attention  to  the  calling 


84 


A  DICTIONARY  OP  ELECTRICAL 


subscriber,  or  to  the  falling  of  a  drop,  are  generally  added. 
(See  Annunciators.    Bell  Call,  Electric.) 

(3)  Connecting  Cords  and  Keys  for  connectiong  the  opera- 
tor's telephone,  and  means  for  ringing  subscribers'  bells,  and 
clearing  out  drops. 


In  Electric  Light  Switch-Boards,  or  Distributing  Switches, 
spring-jack  contacts  are  connected  with  the  terminals  of  dif- 
ferent circuits,  and  plug-switches  with  the  dynamo  terminals. 
By  these  means,  any  dynamo  can  be  connected  with  any  cir- 
cuit, or  a  number  of  circuits  can  be  connected  with  the  same 
dynamo,  or  a  number  of  separate  dynamos  can  be  placed 
in  the  same  circuit,  without  interference  with  the  lights. 


WORDS,   TERMS  AND  PHRASES.  85 

ISoal,  Electric A  boat  provided  with  electric  mo- 
tive power. 

Electric  power  has  been  applied  both  for  ordinary  vessels 
and  for  sub-marine  torpedo  boats. 

Bobbins,  Electric An  insulated  coil  of  wire  for 

an  electro-magnet.    (Sec  Coils,  Electric.) 

Body  l*rotector,  Electric A  device  for  pro 

tccting  the  human  body  against  the  accidental  passage  of 
an  electric  discharge. 

To  protect  the  human  body  from  the  acci- 
dental passage  through  it  of  dangerous  elec- 
tric currents,  Delany  places  alight,  flexible, 
conducting  wire,  A  A  B  L  L,  in  the  posi- 
tion shown  in  Fig,  60,  for  the  purpose  of 
leading-  the  greater  part  of  the  current 
around  instead  of  through  the  body. 

Inside  insulating  shoe-soles  for  lessen- 
ing the  danger  from  accidental  contacts 
through  grounded  circuits  have  also  been 
proposed. 

Boiler-Feed,  Electric A  device  for  automatic- 
ally opening  a  boiler-feed  apparatus  electrically,  when  the 
water  in  the  boiler  falls  to  a  certain  predetermined  point. 

Bole. — A  unit  recently  proposed  by  the  British  Associa- 
tion. 

One  bole  is  equal  to  one  gramme-kine. 

Bolometer,  or  Laiigley's  Thermic  Balance.— An 
apparatus  for  determining  small  differences  of  temperature, 
constructed  on  the  principle  of  the  differential  galvanometer. 
(See  Galvanometer,  Differential.) 

A  coil  composed  of  two  separate  insulated  wires,  wound  to- 
gelher,  is  suspended  in  a  magnetic  field,  and  has  a  current  sent 
through  it.  Under  normal  conditions,  this  current  separates 
into  two  equal  parts,  and  runs  through  the  wires  in  opposite 


86  A  DICTIONARY   OF   ELECTRICAL 

directions.     It  therefore  produces  no  sensible  field,  and  suffers 
no  deflection  by  the  lield  in  which  it  is  suspended. 

Any  local  application  of  heat,  however,  causing  a  difference 
in  resistance,  prevents  this  equality.  A  field  is  therefore  pro- 
duced in  the  suspended  coil,  which,  though  extremely  small, 
is  rendered  measurable  by  means  of  the  powerful  field  pro- 
duced in  the  coil,  within  which  the  double  coil  is  suspended. 

Differences  of  temperature  as  small  as  degree  F.  are 

detected  by  the  instrument. 

Bombardment,  Molecular The  forcible  rec- 
tilinear projection  of  molecules  in  exhausted  vessels,  that 
takes  place  from  the  negative  electrode,  on  the  passage  of 
electric  discharges]  (See  H atter,  Radiant.) 

Boreal  Magnet  Pole. — A  name  sometimes  employed  in 
France  for  the  south-seeking  pole  of  a  magnet,  as  distin- 
guished from  the  austral,  or  north-seeking  pole. 

That  pole  of  a  magnet  which  points  toward  the  geo- 
graphical south. 

If  the  earth's  magnetic  pole  in  the  Northern  Hemisphere  be 
of  north  magnetism,  then  the  pole  of  a  needle  that  points  to 
it  must  be  of  the  opposite  polarity,  or  of  south  magnetism. 
In  this  country  we  call  the  end  which  points  to  the  north  the 
north-seeking  end,  or  the  marked  pole.  In  France,  the  end 
which  points  to  the  north  is  called  the  austral  pole.  Austral 
means  south  pole.  (See  Austral  Magnet  Pole.) 

The  austral  is  therefore  the  north-seeking  pole,  and  the 
boreal,  the  south-seeking  pole. 

Bouclieriziiig.— A  process  adopted  for  the  preservation 
of  wooden  telegraph  poles,  by  injecting  a  solution  of  copper 
sulphate  into  the  pores  of  the  wood.  (See  Poles,  Telegraphic.) 

Bound  and  Free  Charge.— The  condition  of  an  elec- 
tric cha.'-g;  on  a  conductor  placed  near  another  conductor, 


WORDS,   TERMS  AND  PHRASES.  87 

but  separated  from  it  by  a  medium  through  which  electro- 
static induction  can  take  place.  (See  Induction,  Electrostatic.) 

The  charge,  on  a  completely  isolated  conductor,  readily 
leaves  it  when  put  in  contact  with  a  good  conductor  con- 
nected with  the  ground.  The  charge  in  this  condition  is 
called  a,  free  charge.  When,  however,  the  conductor  is  placed 
near  another  conductor,  but  separated  from  it  by  a  medium 
through  which  induction  can  take  place,  a  charge  of  the  oppo- 
site name  is  induced  in  the  neighboring  conductor.  This 
charge  is  he-Id  or  bound  on  the  conductor  by  the  mutual  at- 
traction of  the  opposite  charges. 

To  discharge  a  bound  charge,  both  conductors  must  be  sim- 
ultaneously touched  by  any  good  conducting  substance.  The 
bound  charge  was  formerly  called  dissimulated  or  latent  elec- 
tricity. (See  Charge.  Dissimulated  or  Latent  Electricity.) 

Box  Bridge.— (See  Balance,  Wheatstone's  Electric,  Box 
Form  of.) 

Box,  Distribution for  Electric  Arc  Light 

Circuits. — A  device  by  means  of  which  arc  and  incandescent 
lights  may  be  simultaneously  employed  on  the  same  line; 
from  a  constant  current  dynamo  electric-machine  or  other 
source. 

A  portion  of  the  line  circuit,  whose  difference  of  potential 
is  suilicient  to  operate  the  electro- receptive  device,  as  for  ex- 
ample an  incandescent  lamp,  is  divided  into  such  a  number 
of  multiple  circuits  as  will  provide  a  current  of  the  requisite 


Fig. 

strength  for  each  of  the.  devices.  In  order  to  protect  the  re- 
maining of  these  devises  so  interpolated,  on  the  i-xt in-uisli- 
ment  of  any  of  the  devices,  automatic  cut-outs  are  provided 


88  A  DICTIONARY   OF  ELECTRICAL 

which  divert  the  current  thus  cut  off  through  a  resistance 
equivalent  to  that  of  the  device. 

A  variety  of  distribution  boxes  are  in  use. 

The  character  of  circuit  employed  in  connection  with  dis- 
tribution boxes  is  shown  in  Fig.  61.  (See  Circuits,  Varieties 
of.) 

Box,  Resistance A  box  containing  a  number  of 

standardized  resistance  coils. 

The  resistance  box  and  coils  are  of  the  same  general  con- 
struction as  the  Box  Bridge.  (See  Balance,  Wheatstone's 
Electric,  Box  Form  of.) 

Braeket,  Lamp A  device  for  holding  or  sup- 
porting an  electric  lamp,  similar  to  a  bracket  for  a  gas  burner. 


Fig.  64. 

Lamp  brackets  are  either  fixed  or  movable.  Those  shown 
in  Figs.  62  and  63  are  fixed.  That  shown  in  Fig.  64  is  mov- 
able. 

Brackets,  Telegraphic or  Arms.— The  sup- 
ports or  cross  pieces  on  telegraph  poles,  provided  for  the 
insulators  of  telegraphic  lines. 


WORDS,    TERMS  AND  PHRASES. 


Telegraphic  insulators  are  supported  either  on  wooden  arms, 
or  on  iron  or  metal  brackets. 


Fig.  66. 

Fig.  65,  shows  a  form  of  iron  bracket.  Fig.  66,  shows  a 
form  of  wooden  arm. 

Various  well  known  modifications  of  these  shapes  are  in 
common  use.  For  details  see  Telegraph  Poles. 

Brake,  Electro-Magnetic A  brake  for  car 

wheels,  the  braking  powers  for  which  is  either  derived  from 
electro-magnetism,  or  is  thrown  into  action  by  electro-mag- 
netic devices. 

Electro-magnetic  car  brakes  are  of  a  great  variety  of  forms. 
They  may,  however,  be  arranged  in  two  classes,  viz. : 

(1)  Those  in  which  magnetic  adhesion  or  the  magnetic  at- 
traction of  the  wheels  to  the  brake  is  employed. 

(2)  Ordinary  brake  mechanism  in  which  the  force  operating 
the  brake  is  thrown  into  action  by  an  electro-magnet. 

IS ra k<- .  Proiiy  or  Friction A  mechanical  de- 
vice for  measuring  the  power  of  a  driving  shaft. 


A  DICTIONARY  OF  ELECTRICAL 


An  inflexible  beam,  Fig.  67,  is  provided  at  one  end  with  a 
clamping  device  for  clamping  the  driving  shaft,  and  at  the 
other  end  A,  with  a  pan  for  holding  weights. 

If  the  brake  be  arranged  as 
shown    in  Fig.   67,   and    the 
A  shaft  rotate  in  the  direction 
A    of  the  arrow,  the  tendency  is 
^  \  to  carry  the  beam  around  with 
it,  placing  it  at  one  moment 
fig.  67.  in  the  position  shown  by  the 

dotted  line.  If  a  sufficiently  heavy 
weight  be  placed  at  x,  in  a  pan 
hung  at  A,  the  beam  will  assume 
a  vertical   position  downwards.       |r~ 
If,  however,  the  torque,  or  twist-  _^jp 
ing  force  of  the  driving  shaft  be       L 
balanced  by  the  weight,  the  bar 
will    remain    horizontal.       The 
power  can  then  be  calculated  by 
multiplying  the  weight  in  pounds 

V-  — "a— \ 


Fig.  i 


by  the  circumference  in  feet 
of  the  circle  of  which  the  bar  is 
a  radius,  and  this  product  by  the 
number  of  turns  of  the  driving 
shaft  per  minute.  The  product 
will  be  the  number  of  foot- 
pounds per  minute,  and,  when 
divided  by  33,000,  will  give  the 

Horse-Power.    (See  Horse-Power.) 
Some  modified  forms  of  the  Prony  Brake  are  shown  in  Figs. 

68,  and  69. 

Branch-Block. — A  device  employed  in  electric  wiring 
for  taking  off  a  branch  from  a  main  circuit. 
Breaking    Weight    of   Telegraph    Wires.— The 

weight  which  when  hung  at  the  end  of  a  wire  will  break  it. 


WORDS,   TEKMS  AND  PHRASES.  91 

Ordinary  copper  wire  will  break  at  about  17  tons  to  the 
square  inch  of  cross-section.  Common  wrought  iron  breaks  at 
25  tons  to  the  square  inch.  When  drawn,  the  breaking  weight 
is  often  as  great  as  40  or  50  tons  to  the  square  inch.  These 
figures  are  to  be  regarded  as  approximate  only,  since  differ- 
ences in  the  physical  conditions  of  metals,  as  well  as  slight 
variations  in  their  chemical  composition,  often  produce  marked 
differences  in  their  breaking  weights. 

Breath  Figures,  Electric (See  Figures,  Elec- 
tric or  Breath.) 

Bridge,  Electric (See  Balance,  Wheatstone's 

Electric.) 

Bridge,  Magnetic An  apparatus  invented  by 

Edison  for  measuring  magnetic  resistance,  similar  in  principle 
to  Wheatstone's  Electric  Bridge. 


Fig.  70. 

The  magnetic  bridge  is  based  on  the  fact  that  two  points  at 
the  same  magnetic  potential  fail,  when  connected,  to  produce 
any  action  on  a  magnetic  needle.  The  magnetic  bridge  may 
be  arranged  as  shown  in  Fig.  70,  of  four  sides  made  of  pure, 
soft  iron.  The  poles  of  an  electro-magnet  are  connected,  as 
shown,  to  projections  atllie  middle  of  the  short  side  of  the 
rectangle.  By  this  means  a  difference  of  magnetic  potential  is. 


93  A  DICTIONARY  OF  ELECTRICAL 

maintained  at  these  points.  The  two  long  sides  are  formed 
of  two  halves  each,  which  form  the  four  arms  of  the  balance. 
Two  of  these  only  are  movable. 

Two  curved  bars  of  soft  iron,  of  the  same  area  of  cross-sec- 
tion as  the  arms  of  the  bridge,  rest  on  the  middle  of  the  long 
arms,  in  the  arched  shape  shown.  Their  ends  approach  near 
the  top  of  the  arch  within  about  a  half  inch.  A  space  is  hol- 
lowed out  between  these  ends,  for  the  reception  of  a  short 
needle  of  well-magnetized  hardened  steel,  suspended  by  a  wire 
from  a  torsion  head. 

The  movements  of  the  needle  are  measured  on  a  scale  by  a 
spot  of  light  reflected  from  a  mirror. 

The  electro-magnet  maintains  a  constant  difference  of  mag- 
netic potential  at  the  two  shorter  ends  of  the  rectangle.  If, 
therefore,  the  four  bars,  or  arms  of  the  bridge,  are  magneti- 
cally identical,  there  will  be  no  deflection,  since  no  difference 
of  potential  will  exist  at  the  ends  of  the  bars  between  which 
the  needle  is  suspended.  If  one  of  the  bars  or  arms,  how- 
ever, be  moved  even  a  trifle,  the  needle  is  at  once  deflected, 
the  motion  becoming  a  maximum  when  the  bar  is  entirely  re- 
moved. If  replaced  by  another  bar,  differing-  in  cross-section, 
constitution,  or  molecular  structure,  the  balance  is  likewise 
disturbed. 

The  magnetic  bridge  is  very  sensitive.  It  was  designed 
by  its  inventor  for  testing  the  magnetic  qualities  of  the  iron 
used  in  the  construction  of  dynamo-electric  machines. 

Bridge,  Whcatstoii c's  Electric (See  Wheat- 
stone's  Balance,  Electric.) 

Broken  Circuit.— An  open  circuit. 

A  circuit,  the  electrical  continuity  of  which  has  been  broken, 
and  through  which  "the  current  has  therefore  ceased  to  pass. 

Broken  Circuit.— (See  Circuit,  Broken.) 

Brush  Discharge —  —The  faintly  luminous  dis- 
charge that  occurs  from  a  pointed  positive  conductor.  (See 
Discharge,  Connective.) 


WORDS,   TERMS  AND  PHRASES.  93 

Brush,  Faradic — An  electrode  in  the  form  of  a 

brush  employed  in  the  medical  application  of  electricity. 
The  bristles  are  generally  made  of  nickelized  copper  wire. 
Brush  Holders  for  Dynamo-Electric  Machines. 

— Devices  for  supporting  the  collecting  brushes  of  dynamo- 
electric  machines. 

As  the  brushes  require  to  be  set  or  placed  on  the  commu- 
tator in  a  position  which  often  varies  with  the  speed  of  the 
machine,  and  with  changes  in  the  external  circuit,  all  brush 
holders  are  provided  with  some  device  for  moving  them  con- 
centrically with  the  commutator  cylinder. 

Brushes,    Adjustment    of  the of  Dyiiamo- 

Elccl  ric  Machines. — Shifting  the  brushes  into  the  required 
posit  ion  on  the  commutator  cylinder,  either  non-automatically 
by  hand,  or  automatically  by  the  current  itself.  (See  Auto- 
matic Regulation  of  Dynamo-Electric  Machines.) 

Brushes  for  Dynamo-Electric  Machines.— Strips 
of  metal,  bundles  of  wire,  or  slit  plates  of  metal,  or  carbon, 
that  bear  on  the  commutator  cylinder 
and  curry  of!'  the  current  generated. 

Rotating  brushes  consisting  of  metal 
discs  arc  sometimes  employed.  Copper 
is  almost  universally  used  for  the 
brushes  of  dynamo-electric  machines. 

The  brush  shown  at  B,  Fig.  71,  is 
formed  of  copper  wires,  soldered  to- 
gether at  the  non-bearing  end.  A.  cop- 
per plate,  slit  at  the  bearing  end,  is 
shown  at  C,  and  bundles  of  copper 
plates,  soldered  together  at  the  non- 
hearing  end,  are  shown  at  D. 

The  brushes  should  bear  against  the 
commutator  cylinder  with  sufficient 
force  1o  prevent  jumping,  and  conse-  Fig. "I. 

quent  burning,  and  yet  not  so  hard  as  to  cause  excessive  wear. 


U-1 


A  DICTIONARY  OF  ELECTRICAL 


Brushes,  Lead  of 


— The  angle  through  which 


the  brushes  of  a  dynamo-electric  machine  must  be  moved  for- 
wards, or  in  the  direction  of  rotation,  in  order  to  diminish 
sparking  and  to  get  the  best  output  from  the  dynamo. 

The  necessity  for  the  lead  arises  from  the  counter  magnetism 
of  the  armature,  and  the  magnetic  lag  of  its  iron  core.  (See 
Angle  of  Lead.) 

Brushes,  Scratch Brushes  made  of  wire  or  stiff 

bristles,  etc.,  suitable  for  cleaning  the  surfaces  of  metallic 
objects  before  placing  them  in  the  plating  bath. 

These  brushes  are  of  various  shapes  and  are  provided  with 
wires  or  bristles  of  varying  coarseness. 

Buoy,  Electric A  buoy,   on  which  luminous 

electric  signals  are  displayed. 
Bun  son's  Voltaic  Cell.— (See  Cell,  Voltaic.) 

Burner,  Eleclrfrc A  gas- 
burner  whose  gas-jet  is  electrically  ignited^ 
On  pulling  the  pendant  C,  Fig.  72,  a  spark 
from  a  spark  coil  ignites  the  gas.  On  pull- 
ing the  slide  the  gas  is  turned  off.  (See 
Argand  Burner.) 

Burner,  Automatic  Eleclric 

—An  electric  device  for  either  turning  on 
the  gas  and  lighting  it,  or  for  turning  it  off. 
One  push-button,   usually  a  white  one, 
turns  the  gas  on  and  lights  it  by  means  of 
a  succession  of  sparks  from  a  spark  coil. 
Another  push-button,  usually  a  black  one, 
turns  the  gas  off.     Automatic  burners  are 
also  made  with  a  single  button. 
Burglar  Alarm.— (See  Alarm,  Electric,  Burglar.) 
Burnetizing.— A  method  adopted  for  the  preservation  of 
wooden  telegraph  poles  by  injecting  a  solution  of  zinc  chlor- 
ide into  the  pores  of  the  wood.     (See  Poles,  Telegraphic.) 


WORDS,   TERMS  AND  PHRASES. 


Burning  at  Commutator  of  Dynamo.— An  arcing 
at.  the  brushes  of  u  dynamo-electric  machine,  due  to  their  im- 
perfect contact,  or  improper  position,  which  results  in  loss  of 
energy  and  destruction  of  the  commutator  segments. 

Butt  Joint.— (See  Joint,  Butt.) 

Button,  I*usli A  device  for  closing  an  electric 

circuit  by  the  movement  of  a  button. 

A  button,  when  pushed  by  the  hand,  closes  a  contact,  and 
thus  completes  a  circuit  in  which  some  electro-receptive  device 
is  placed.  This  circuit  is  opened  by  a  spring,  on  the  removal 
of  the  pressure.  Some  forms  of  push-buttons  are  shown  in 
Figs.  73  and  73a. 


Fig.  73. 


Fig.  V,. 


A  floor-push  for  dining-rooms  and  offices  is  shown  in  Fig. 
74. 

B.  W.  CJ. — A  contraction  for  Birmingham  Wire  Gauge. 
(See  Wire  Gauge.) 

Buzzer,  Electric  —  —A  call,  not  as  loud  as  that  of  a 
bell,  produced  by  an  automatic  make  and  break.  (See 
Alarms,  Electric.) 

Cable  Armor— (See  Armor  of  Cable.) 

Cable  Clip.— (See  Cable  Hanger.) 


96  A  DICTIONARY  OF  ELECTRICAL 

Cable  Core.— (See  Core  of  Cable.) 

Cable,  Aerial  —  —A  cable  for  telegraphic  or  tele- 
phonic communication,  suspended  in  the  air  from  suitable 
poles. 

Cable,  Electric A  conductor  containing  either 

a  single  conductor,   or    two    or  more    separately    insulated 
electric  conductors. 

Strictly  speaking,  the  word  cable  should  be  limited  to  the 
case  of  more  than  a  single  conductor.  Usage,  however, 
sanctions  the  employment  of  the  word  to  indicate  a  single 
insulated  conductor. 

The  conducting  wire  may  consist  of  a  single  wire,  of  a 
number  of  sepai'ate  wires  electrically  connected,  or  of  a  num- 
ber of  separate  wires  insulated  from  one  another. 

An  electric  cable  con- 
sists of  the  following 
parts,  viz.  : 

(1)  The    conducting 
wire  or  core. 

(2)  The    insulating 
material  for  separating 
the  several  wires,  and 

(3)  An  armor  or  pro- 
tecting covering,   con- 
sisti  ng  of  strands  of  iron 
wire,  or  of  a  metallic 
coating  or  covering  of 
lead. 

As  to  their  position, 
cables  are,  aerial,  sub- 
marine,  or  under- 

„.    _r^™       ^^^^™     ground.     As    to    their 
purpose,  they  are  tele- 
graphic, telephonic,  or  electric  light  and  pmi-er  cables. 

Fig.  75  shows  a  form  of  submarine  cable  in  which  the  armor 
is  formed  of  strands  of  iron  wire. 


WORDS,   TERMS  AND  PHRASES. 


97 


Cablegram.— A  message  received  by  means   of  a  sub- 
marine telegraphic  cable. 

Cable  Hanger.— A  hanger  or  hook,  suitably  secured  to 
the  cable,  and  designed  to  sustain  its 
weight  by  intermediately  supporting  it 
on  iron  or  steel  wires. 

A  cable  hanger,  or  cable  clip,  is 
shown  in  Fig.  76. 

The  weight  per  foot  of  an  aerial  cable 
is  generally  so  great  that  the  poles  or 
supports  would  require  to  be  very  near 
together,  unless  the  device  of  inter- 
mediate supports,  by  means  of  cable 
clips,  were  adopted 

Cable  Serving.— Strands  of  tarred 
hemp  or  jute,  wrapped  around  the  in- 


Fig.  76. 


sulated  core  of  a  cable,  to  protect  it  from  the  pressure  of  the 
metallic  armor. 


Cables,  Sub 

under  water. 


ine 


—Cables   designed    for    use 


These  are  either  shallow -water,  or  deep-sea  cables.  Gutta- 
percha  answers  admirably  for  the  insulating  material  of  the 
core.  Various  other  insulators  are  also  used. 

Strands  of  tarred  hemp  or  jute,  known  as  the  cable-serving, 
are  wrapped  around  the  insulated  core,  to  protect  it  from  the 
pressure  of  the  galvanized  iron  wire  armor  afterwards  put  on. 
To  prevent  corrosion  of  the  iron  wire,  it  is  covered  with  tarred 
hemp,  galvanized,  or  otherwise  coated. 

Cables,  Underground  —  —Cables  designed  for  use 
underground. 

These  are  either  placed  directly  in  the  ground,  or  in  con-. 
duits,  or  subways,  especially  prepared  to  receive  them.  (See 
Conduit,  Electric  Underground.  Subway,  Electric.) 

Calibration,  Absolute  and  Relative of  In- 
strument.— The  determination  of  the  absolute  or  the  rela- 


98  A  DICTIONARY  OF  ELECTRICAL 

tive  values  of  the  reading  of  an  electrometer,  galvanometer, 
voltmeter,  amperemeter,  01*  other  similar  instrument. 

The  calibration  of  a  galvanometer,  for  example,  consists  in 
the  determination  of  the  law  that  governs  its  different  de- 
flections, and  by  which  is  obtained  in  amperes,  either  the  ab- 
solute or  the  relative  current  required  to  produce  such 
deflections.  » 

For  various  methods  of  calibration,  see  standard  works  on 
Electrical  Testing,  or  on  Electricity. 

Calibration,  Invariable of  Galvan- 
ometer.— In  galvanometers  with  absolute  calibration,  a 
method  for  preventing  the  occurrence  of  variations  in  the  in- 
tensity of  the  field  of  the  galvanometer,  due  to  the  neighbor- 
hood of  masses  of  iron,  etc. 

Callaud  Voltaic  Cell.— (See  Cell,  Voltaic.) 

Call-Bell,  Electric (See  Alarm,  Electric.  Bell- 
Call,  Electric.) 

Caloric.— A  term  formerly  applied  to  the  fluid  that  was 
believed  to  be  the  cause  or  essence  of  heat. 

The  use  of  the  word  caloric  at  the  present  time  is  very 
unscientific,  since  heat  is  now  known  to  be  an  effect  and  not  a 
material  thing.  (See  Heat.) 

Calorie,  or  Calory.— A  heat  unit 

There  are  two  calories,  the  small  and  the  large  calorie. 

The  amount  of  heat  required  to  raise  the  temperature  of  one 
gramme  of  water,  1°  C.  is  called  the  small  calorie. 

Sometimes  the  term  is  used  to  mean  the  amount  of  heat 
required  to  raise  1,000  grammes  of  water  1°  C.  This  is  called 
the  large  calorie.  The  first  usage  of  the  word  is  the  com- 
monest. 

Calorescence.— The  transformation  of  invisible  heat-rays 
into  luminous  rays,  when  received  by  certain  solid  substances. 

The  term  was  proposed  by  Tyndall.  The  light  and  heat 
from  a  voltaic  arc  are  passed  through  a  hollow  glass  lens 
filled  with  a  solution  of  iodine  in  bisulphide  of  carbon. 


WORDS,  TERMS  AND  PHRASES.  99 

This  solution  is  opaque   to  light  but  quite  transparent  to 
heat. 

If  a  piece  of  charred  paper,  or  thin  platinum  foil,  is  placed 
in  the  focus  of  these  invisible  rays,  it  will  be  heated  to  brilliant 
incandescence.  (See  Focus.) 

Calorimeter. — An  instrument  for  measuring  the  quan- 
tity of  heat  possessed  by  a  given  weight  or  volume  of  a  body 
at  a  given  temperature. 

Thermometers  measure  temperature  only.  A  thermometer 
plunged  in  a  cup  full  of  boiling  water  shows  the  same  temper- 
ature that  it  would  in  a  tub  full  of  boiling  water.  The  quantity 
of  heat  present  in  the  two  cases  is  of  course  greatly  different 
and  can  be  measured  by  calorimeters  only. 
Various  forms  of  Calorimeters  are  employed. 
In  order  to  determine  the  quantity  of  heat  in  a  given 
weight  of  any  body,  this  weight  may  be  heated  to  a  definite 
temperature,  such  as  the  boiling  point  of  water,  and  placed  in  a 
vessel  containing  ice,  and  the  quantity  of  ice  melted  by  the 
body  in  cooling  to  the  temperature  of  the  ice,  is  determined 
by  measuring  the  amount  of  water  derived  from  the  melting 
of  the  ice.  Care  must  be  observed  to  avoid  the  melting  of  the 
ice  by  external  heat. 

In  this  way  the  amount  of  heat  required  to  raise  the  tem- 
perature of  a  given  weight  of  a  body  a  certain  number  of  de- 
grees, or  the  capacity  of  the  body  for  heat,  may  be  compared 
with  the  capacity  of  an  equal  weight  of  water.  This  ratio  is 
called  the  Specific  Heat.  (See  Heat,  Specific.) 

The  heat  energy,  present  in  a  given  weight  of  any  substance 
at  a  given  temperature,  can  be  determined  by  means  of  a 
calorimeter ;  for,  since  a  pound  of  water  heated  1°  F.  absorbs 
an  amount  of  energy  equal  to  772  foot-pounds,  the  energy  can 
be  readily  calculated  if  tin-  mimbfi-  of  pounds  of  water  and  the 
number  of  degrees  of  temperature  are  known.  (See  Me- 
chanical Equivalent  of  Heat.) 


100 


A  DICTIONARY  OF  ELECTRICAL 


Calorimeter,  Electric 


— An  instrument  for  meas- 


uring the  heat  developed  in  a  conductor,  in  a  given  time,  by 
an  electric  current. 

A  vessel  containing  water,  is 
provided  with  a  thermometer  T, 
Fig.  77.  The  electric  current 
passes  for  a  measured  time 
through  a  wire  N  M,  immersed 
in  the  liquid. 

The  quantity  of  heat  is  deter- 
mined   from    the    increase     of 
,x  temperature,  and  the  weight  of 
the  water. 

According  to  Joule,  the  num- 
ber of  heat  units  (See  Heat  Un- 
ftSf  English)  developed  in  a  con- 
ductor by  an  electric  current  is  proportional, 

1.  To  the  Resistance  of  the  Conductor. 

2.  To  the  Square  of  the  Current  passing. 

3.  To  the  Time  the  current  is  passing. 

The  heating  power  of  a  current  is  as  the  square  of  the  cur- 
rent only  when  the  resistance  remains  the  same.  (See  Heat, 
Electric.) 

Calorimetric  Photometer. — (See  Photometer,  Calori- 
metric.) 

Candle,  Electric A  term  applied  to  the  Jab- 

lochkoff  candle,  and  other  similar  devices. 

The  Jablochkoff  electric  candle  consists  of  two 
parallel  carbons,  separated  by  a  layer  of  kaolin 
or  other  heat-resisting  insulating  material,  as 
shown  in  Fig.  78.  The  current  is  passed  into 
and  out  of  the  carbons  at  one  end  of  the  candle, 
and  forms  a  voltaic  arc  at  the  other  end.  In 
order  to  start  the  arc,  a  thin  strip  called  the  igniter, 
consisting  of  a  mixture  of  some  readily  ignitable 
substance,  connects  the  upper  ends  of  the  carbons.  Fig.  78, 


WORDS,  TERMS  AND  PHRASES.  101 

An  alternating  current  is  generally  employed  with  these 
candles,  thus  avoiding  the  difficulty  which  would  otherwise 
occur  from  the  more  rapid  consumption  of  the  positive  than 
the  negative  carbon.  (See  Current,  Alternating.) 

Candle,  Foot A  unit  of  illumination  equal  to 

the  illumination  produced  by  a  standard  candle  at  the  distance 
of  one  foot.  Proposed  by  Hering. 

According  to  this  unit,  the  illumination  produced  by  a  stand- 
ard candle  at  the  distance  of  two  feet  would  be  but  the  one- 
fourth  of  a  foot-candle  ;  at  three  feet,  the  one-ninth  of  a  foot- 
candle,  etc. 

The  advantage  of  the  proposed  standard  lies  in  the  fact 
that  knowing  the  illumination  in  foot-candles  required  for  the 
particular  work  to  be  done,  it  is  easy  to  calculate  the  position 
and  intensity  of  the  lights  required  to  produce  the  illumina- 
tion. 

Candle,  Metre The  illumination  produced  by 

a  standard  candle  at  the  distance  of  one  metre. 

Candle,  Standard A  candle  of  definite  compo- 
sition which,  with  a  given  consumption  in  a  given  time,  will 
produce  a  light  of  a  fixed  and  definite  brightness. 

A  candle  which  burns  120  grains  of  spermacetti  wax  per 
hour,  or  2  grains  per  minute,  will  give  an  illumination  equal 
to  one  standard  candle. 

Candle,  A ,  or.  Unit  of  Photometric  Mea§- 

uremenl.— The  unit  of  photometric  intensity. 

Such  a  light  as  would  be  produced  by  the  consumption  of 
two  grains  of  a  standard  candle  per  minute. 

An  electric  lamp  of  16  candle-power,  or  one  of  2,000  candle- 
power,  is  a  light  that  gives  respectively  16  or  2,000  times  as 
bright  a  light  as  that  of  one  standard  candle. 

Capacity,  Dielectric (See  Dielectric  Capacity.) 

Capacity,  Electrostatic The  ability  of  a  con- 

LTFRAKY 

OF  CALIFORNIA 

SAKTA  BARBARA 


102  A  DICTIONARY  OP  ELECTRICAL 

ductor  or  condenser  to  hold  a  certain  quantity  of  electricity 
at  a  certain  potential. 

The  electrostatic  capacity  of  a  conductor,  or  of  a  condenser, 
Is  measured  by  the  quantity  of  electricity  which  must  be  given 
it  as  a  charge,  in  order  to  raise  its  potential  a  certain  amount. 
(See  Condenser.  Potential.)  In  this  respect  the  electrostatic 
capacity  of  a  conductor  is  not  unlike  the  capacity  of  a  vessel 
filled  with  a  liquid  or  gas.  A  certain  quantity  of  liquid  will 
fill  a  vessel  to  a  level  dependent  on  the  size  or  capacity  of  the 
vessel.  In  the  same  manner  a  given  quantity  of  electricity 
will  produce,  in  a  conductor  or  condenser,  a  certain  difference 
of  electric  level  dependent  on  the  electrical  capacity  of  the  con- 
ductor or  condenser. 

Or,  the  quantity  of  gas  that  can  be  forced  into  a  vessel  de- 
pends on  the  size  of  the  vessel  and  the  pressure  with  which  it 
is  forced  in.  A  tension  or  pressure  is  thus  produced  by  the 
gas  on  the  walls  of  the  vessel  that  is  greater,  the  smaller  the 
size  of  the  vessel,  and  the  greater  the  quantity  forced  in. 

In  the  same  manner,  the  smaller  the  capacity  of  a  conduc- 
tor, the  smaller  is  the  charge  required  to  raise  it  to  a  given 
potential,  or  the  higher  the  potential  a  given  charge  will 
raise  it. 

The  capacity  K,  of  a  conductor  or  condenser,  is  therefore 
directly  proportional  to  the  charge  Q,  and  inversely  propor- 
tional to  the  potential  V,  or 

Q 

K  =-   . 
V 

From  which  we  obtain  Q  =  KV;  or, 

The  quantity  of  electricity,  required  to  charge  a  conductor 
or  condenser  to  a  given  potential,  is  equal  to  the  capacity  of 
the  conductor  or  condenser  multiplied  by  the  potential  through 
which  it  is  raised. 

Capacity,  Electro§tatic Unit    of ;    The 

Farad. — A  conductor  or  condenser  of  such  a  capacity  that 


WORDS,  TERMS  AND  PHRASES.  103 

an  electro-motive  force  of  one  volt  will  charge  it  with  a  quan- 
tity of  electricity  equal  to  one  coulomb.     (See  Farad.) 
Capacity  of  Polarization  of  a  Voltaic  Cell.— The 

quantity  of  electricity  required  to  be  discharged  by  a  voltaic 
cell  in  order  to  produce  a  given  polarization.  (See  Cell,  Vol- 
taic. Polarization  of  Negative  Plate.} 

During  the  discharge  of  a  voltaic  battery,  an  electro-motive 
force  is  gradually  set  up  that  is  opposed  to  that  of  the  battery. 
The  quantity  of  electricity  required  to  produce  a  given  polariza- 
tion, depends,  of  course,  on  the  condition  and  size  of  the 
plates.  Such  a  quantity  is  called  the  Capacity  of  Polarization. 

Capacity  of  a  Telegraph  Line  or  Cable.— The 
ability  of  a  wire  or  cable  to  permit  a  certain  quantity  of  elec- 
tricity to  be  passed  into  it  before  acquiring  a  given  difference 
of  potential. 

Before  a  telegraph  line  or  cable  can  transmit  a  signal  to 
its  further  end,  its  difference  of  potential  must  be  raised  to  a 
definite  amount  dependent  on  the  character  of  the  instru- 
ments and  the  nature  of  the  system. 

The  first  effect  of  a  given  quantity  of  electricity  being 
passed  into  a  line,  is  to  produce  an  accumulation  of  electricity 
on  the  line,  similar  to  the  charge  in  a  condenser.  Cables 
especially  act  as  condensers,  and  from  the  high  specific  induc- 
tive capacity  of  the  insulating  materials  employed,  permit 
considerable  induction  to  take  place  between  the  core,  and 
the  metallic  armor  or  sheathing,  or  the  ground. 

The  capacity  of  a  cable  depends  on  the  capacity  of  the 
wire;  i.e.,  on  its  length  and  surface,  on  the  specific  inductive 
capacity  of  its  insulation,  and  its  neighborhood  to  the  earth, 
or  to  other  conducting  wires,  casings,  armors,  or  metallic 
coatings.  Submarine  or  underground  cables  therefore  have 
a  greater  capacity  than  air  lines. 

This  accumulation  of  electricity  produces  a  retardation  in 
tha  speed  of  signaling,  because  the  wire  must  be  charged  be- 
fore the  signal  is  received  at  the  distant  end,  and  discharged 


104 


A  DICTIONARY   OF  ELECTRICAL 


or  neutralized  before  a  current  can  be  sent  in  the  reverse 
direction.  This  latter  may  be  done  by  connecting-  each  end  to 
earth,  or  by  the  action  of  the  reverse  currant  itself. 

The  smaller  the  electrostatic  capacity  of  a  cable,  therefore, 
the  greater  the  speed  of  signaling.    (See  Retardation.) 

Capacity,    Specific    Inductive ;  Dielectric 

Capacity,  or  Dieletric  Constant.— The  ability  of  a  dielec, 
trie  to  permit  induction  to  take  place  through  its  mass,  as 
compared  with  the  ability  possessed  by  a  mass  of  air  of  the 
same  dimensions  and  thickness,  under'pre- 
cisely  similar  conditions. 

The  inductive  capacity  of  a  dielectric  is 
compared  with  that  of  air. 

According  to  Gordon  and  others,  the 
specific  inductive  capacities  of  a  few  sub- 
stances compared  with  air,  are  as  follows : 

Air 1.00 

Glass.. .3.013  to  3.258 

Ebonite 2.284 

Gutta-percha 2. 462 

India  rubber 2.220  to  2.497 

Paraffin  (solid) 1.994 

Shellac .2.740 

Sulphur 2.580 

Turpentine .2.160 

Petroleum 2.030  to  2.070 

Carbon  bisulphide 1.810 

Vacuum 0.99941 

Hydrogen 0. 99967 

Carbonic  acid 1.00036 


fig.  70. 


Faraday,  who  proposed  the  term  specific  inductive  capac- 
ity, employed  in  his  experiments  a  condenser  consisting1  of 
a  metallic  sphere  A,  Fig.  79,  placed  inside  a  large  hollow 
sphere  B. 


WORDS,  TERMS  AND  PHRASES.  105 

The  concentric  space  between  A  and  B  was  filled  with 
the  substance  whose  specific  inductive  capacity  was  to  be  de- 
termined. 

Capillarity.— The  elevation  or  depression  of  liquids  in 
tubes  of  small  internal  diameter. 

The  liquid  is  elevated  when  it  wets  the  walls,  and  depressed 
when  it  does  not  wet  the  walls  of  the  tube. 

The  phenomena  of  capillarity  are  due  to  the  molecular  at- 
tractions existing  between  the  molecules  of  the  liquid  for  one 
another,  and  the  mutual  attraction  between  the  molecules  of 
the  liquid  and  those  of  the  walls  of  the  tube. 

Capillarity,  Effects  of,  on  Battery  Cells.— Disturb- 
ing effects  of  the  proper  action  of  a  voltaic  battery  caused  by 
capillary  action. 

These  effects  are  as  follows,  viz. : 

(1)  Creeping,  or  Efflorescence    of    salts.      (See     Creeping. 
Efflorescence.) 

(2)  Oxidation  of  Contacts  and  consequent  introduction  of 
increased  resistance  into  the  battery  circuit.    The  liquid  enters 
the  capillary  spaces  between  the  contact  surfaces  and  oxidizes 
them. 

Capillary  Electrometer.— An  electrometer  in  which 


Fig.  80. 


difference  of  potential  is  measured  by  the  movements  of  a  drop 
of  sulphuric  acid  in  a  horizontal  tube  filled  with  mercury. 
The  horizontal  glass  tube  with  a  drop  of  acid  at  B,  is  shown  in 


106  A  DICTIONARY  OF  ELECTRICAL 

Fig.  80.  The  ends  of  the  tube  are  connected  with  two  vessels, 
M  and  N,  filled  with  mercury.  If  a  current  be  passed  through 
the  tube,  a  movement  of  the  drop  towards  the  negative  pole 
will  be  observed.  Where  the  electro-motive  force  does  not 
exceed  one  volt,  the  amount  of  the  movement  is  proportional 
to  the  electro-motive  force. 

Carbon. — An  elementary  substance  which  occurs  naturally 
in  three  distinct  allotropic  forms,  viz. :  charcoal,  graphite  and 
the  diamond.  (See  Allotropy.) 

Carbon,  Artificial Carbon  obtained  by  the  car- 
bonization of  a  mixture  of  pulverized  carbon  with  different 
carbonizable  liquids. 

Powdered  coke,  or  gas-retort  carbon,  sometimes  mixed  with 
lamp-black  or  charcoal,  is  made  into  a  stiff  dough  with 
molasses,  tar,  or  any  other  hydro-carbon  liquid.  The  mixture 
is  moulded  into  rods,  pencils,  plates,  bars  or  other  desired 
shapes  by  the  pressure  of  a  powerful  hydraulic  press.  After 
drying,  the  carbons  are  placed  in  crucibles  and  covered  with 
lamp-black,  or  powdered  plumbago,  and  raised  to  an  intense 
heat  at  which  they  are  maintained  for  several  hours.  By  the 
carbonization  of  the  hydro-carbon  liquid  the  carbon  paste  be- 
comes strongly  coherent,  and  by  the  action  of  the  heat  its 
conducting  power  increases. 

To  give  increased  density  after  baking,  the  carbons  are 
sometimes  soaked  in  a  hydro-carbon  liquid,  and  subjected  to  a 
re-baking. 

Carbon  Electrodes  for  Arc  Lamps.— Eods  of  artifi- 
cial carbon  employed  in  arc  lamps. 

Carbons  for  arc  lamps  are  generally  copper-coated,  so  as  to 
somewhat  decrease  their  resistance,  and  to  ensure  a  more 
uniform  consumption.  They  are  sometimes  provided  with 
a  central  core  of  soft  carbon,  which  fixes  the  position  of 
the  arc  and  thus  ensures  a  steadier  light.  (See  Carbons, 
Cored.) 


WORDS,  TERMS  AND  PHRASES.  107 

Carbon  Holders  for  Arc  Lamps.— Various  clamping 
devices  for  holding1  the  carbon  electrodes  of  an  arc  lamp  in  the 
lamp  rods. 

Carbon  Telephone  Transmitter.— A  telephone 
transmitter  consisting  of  a  button  of  compressible  carbon. 

The  sound-waves  impart  their  to-and-fro-movements  to  the 

transmitting  diapraghm,  and  this  to  the  carbon  button  thus 

varying  its  resistance  by  pressure.     This  button  is  placed  in 

circuit  with  the  battery  and  induction  coil.     (See  Telephone.) 

Carbonic  Acid  Gas.— A  gaseous  substance  formed  by 

the  union  of  one  atom  of  carbon  with  two  atoms  of  oxygen. 

Carbonic  acid  gas  is  formed  by  the  combustion  of  carbon  in 

a  full  supply  of  air. 

Carbonization,  Processes  of Means  for  suit- 
ably carbonizing  carbonizable  material. 

Carbonizable  material  is  placed  in  suitably  shaped  boxes, 
covered  with  powdered  plumbago  or  lamp-black,  and  subjected 
to  the  prolonged  action  of  intense  heat  while  out  of  contact 
with  air. 

The  electrical  conducting  power  of  the  carbon  which  results 
from  this  process  is  increased  by  the  action  of  the  heat,  and, 
probably,  also  by  the  deposit  in  the  mass  of  the  carbon,  of 
carbon  resulting  from  the  subsequent  decomposition  of  the 
hydro-carbon  gases  produced  during  carbonization. 

When  the  carbonization  is  for  the  purpose  of  producing  con- 
ductors for  incandescent  lamps,  in  order  to  obtain  the 
uniformity  of  conducting  power,  electrical  homogeneity, 
purity  and  high  refractory  power  requisite,  selected  fibrous 
material,  cut  or  shaped  in  at  least  one  dimension  prior  to  car- 
bonization, must  be  taken,  and  subjected  to  as  nearly  uniform 
carbonization  as  possible. 

Carbonized  Cloth  for  High  Resistances.— Discs  of 
cloth  carbonized  by  heating  them  to  an  exceedingly  high  tem- 
perature in  a  vacuum,  or  out  of  contact  with  air. 


108  A  DICTIONARY  OF  ELECTRICAL 

After  carbonization  the  discs  retain  their  flexibility  and 
elasticity  and  serve  admirably  for  high  resistances.  When 
piled  together  and  placed  in  glass  tubes,  they  form  excellent 
variable  resistances  when  subjected  to  varying  pressure. 

Carbons,  Cored for  Arc  Lamps.— A  cylindri- 
cal carbon  electrode  that  is  moulded  around  a  central  core  of 
charcoal,  or  other  softer  carbon. 

These  carbons,  it  is  claimed,  render  the  arc  light  steadier, 
by  maintaining  the  arc  always  at  the  softer  carbon,  and  hence 
at  the  central  point  of  the  electrode. 

A  core  of  harder  carbon,  or  other  refractory  matei-ial,  is 
sometimes  provided  for  the  negative  carbon. 

Carbons,  Concentric,  Cylindrical A  cylin- 
drical rod  of  carbon  placed  inside  a  hollow  cylinder  of  carbon 
but  separated  from  it  by  an  air  space,  or  by 
some  other  insulating,  refractory  material. 

Someti  nes  Jablochkoff  candles  are  made 
with  a  solid  cylindrical  electrode,  concentri- 
cally placed  in  a  hollow  cylindrical  carbon. 

Carcel. — The  light  emitted  by  a  lamp  burn- 
ing 42  grammes  of  pure  colza  oil  per  hour, 
with  a  flame  40  millimetres  in  height. 
One  carcel  =  9.5  to  9.6  standard  candles. 
Carcel  L,amp.— An  oil  lamp  employed  in 
France  as  a  photometric  standard. 
Fig.  81  shows  a  form  of  carcel  lamp. 
Carcel  Standard  Gas  Jet.— A  lighted 
gas  jet  employed  for  determining  the  candle 
power  of  gas  by  measuring  the  height  of  a  jet 
of  gas  burning  under  a  given  pressure,   and 
used  in  connection  with  the  light  of  a  larger 
gas  burner,  burning  under  similar  conditions,  for  the  photo- 
metric measurement  of  electric  lights. 


WORDS,  TEEMS  AND  PHRASES. 


109 


In  Fig-.  82,  is  shown  a  section  of  a  seven-carcel  standard  gas 
jet,  and,  in  Fig.  83,  a  section  of  a  "  candle  burner,"  connected 
with  the  same  service  pipe.  The  gas  for  both  burners  is  re- 
ceived in  a  chamber 
from  whence  it  passes 
by  an  opening  to  the 
burner  under  the  con- 
stant pressure  obtained 
by  the  weight  of  the 
bell  C,  and  the  tube  A. 
The  burner  shown  in 
Fig.  83,  which  is  used  as 
the  standard  of  compar- 
ison, will  give  a  candle 
power  determined  from 
the  height  of  the  jet  of 
the  burning  gas.  This 
height  is  measured  in. 
millimetres  by  a  mov- 
able circular  screen. 

The  determination  of 
the    candle    power    of 


Fig.  S3. 


gas  by  means  of  a  jet  photometer  is  only  approximately  cor- 
rect, unless  many  precautions  are  taken. 

Card,  Compas§ A  card  used  in  a  mariner's  com- 
pass, on  which  are  marked  the  points  of  the  compass.  (See 
Compass  Card.  Azimuth  Compass.) 

Cascade,  Charging  Lcydeii  Jars  by —  —A 

device  for  charging  jars  or  condensers  by  means  of  the  free 
electricity  liberated  by  induction  in  one  coating,  when  a  charge 
is  passed  into  the  other  coating. 

The  jars  are  placed  as  shown  in  Fig.  84,  with  the  inside  coat- 
ing of  one  jar  connected  with  the  outside  coating  of  the  one 
next  it.  There  is  in  reality  no  increase  in  the  entire  charge 
obtained  by  the  use  of  charging  by  cascade  since  the  sum  of  the 


110  A  DICTIONARY  OF  ELECTRICAL 

charges  given  to  the  separate  jars  is  equal  to  the  same  charge 
given  to  a  single  jar  separately  charged. 

The  energy  of  the  discharge  in  cascade  can  be  shown  to  be 
less  than  that  of  the  same  charge  when  confined  to  a  single  jar. 

tf  Q 


Fig.  Sk. 

4  :U  h inn. — A  term  sometimes  used  instead  of  Ration. 

More  correctly  written  Kathion.     (See  Kathion.) 

Cathode. — A  term  sometimes  used  instead  of  Kathode. 

More  correctly  written  Kathode.     (See  Kathode.) 

Caoutchouc,  or  India-rubber.— A  resinous  sub- 
stance obtained  from  the  milky  juices  of  certain  tropical  trees. 

Caoutchouc  possesses  high  powers  of  electric  insulation. 

Cautery,  Electric  or  Galvano-Cautery.  — In  elec- 
tro therapeutics,  the  application  of  platinum  wires  of  various 
shapes,  heated  to  incandescence  by  the  electric  current,  and 
used,  in  place  of  a  knife,  for  removing  diseased  growths,  or 
for  stopping  hemorrhages. 

The  operation,  though  painful  during  application,  is  after- 
wards less  painful  than  that  with  a  knife,  since  secondary 
hemorrhage  seldom  occurs,  and  the  wound  rapidly  heals. 

Galvano-cautery  is  applicable  in  cases  where  the  knife  would 
be  inadmissible  owing  to  the  situation  of  the  parts  or  their 
surroundings. 

Cell,  Voltaic The  combination  of  two  metals,  or 

of  a  metal  and  a  metalloid,  which  when  dipped  into  a  liquid 
or  liquids  called  electrolytes,  and  connected  outside  the  liquid 
by  a  conductor,  will  produce  a  current  of  electricity. 


WORDS,  TERMS  AND  PHRASES.  Ill 

Different  liquids  or  gases  may  take  the  place  of  the  two 
metals,  or  of  the  metal  and  metalloid.  (See  Gas  Battery.) 

Plates  of  zinc  and  copper  dipped  into  a  solution  of  sulphuric 
acid  and  water,  and  connected  outside  the  liquid  by  a  conduc- 
tor form  a  simple  voltaic  cell. 

If  the  zinc  be  of  ordinary  commercial  purity,  and  is  not  con- 
nected outside  the  liquid  by  a  conductor,  the  following  pheno- 
mena occur  : 

(1)  The  sulphuric  acid  or  hydrogen  sulphate,  H2SO4,  is  de- 
composed, zinc  sulphate,  ZnSO4,  being  formed,  and  hydro- 
gen, H8,  liberated. 

(2)  The  hydrogen  is  liberated  mainly  at  the  surface  of  the 
zinc  plate. 

(3)  The  entire  mass  of  the  liquid  becomes  heated. 

If,  however,  the  plates  are  connected  outside  the  liquid  by 
a  conductor  of  electricity,  then  the  phenomena  change  and 
are  as  follows,  viz.  : 

(1)  The  sulphuric  acid  is  decomposed  as  before,  but 

(2)  The  hydrogen  is  liberated  at  the  surface  of  the  copper 
plate  only. 

(3)  The  heat  no  longer  appears  in  the  liquid  only,  but  also 
in  all  parts  of  the  circuit,  and 

(4)  An  electric  current  now   flows  through  the  entire  cir- 
cuit, and  ivill  continue  so  to  flow  as  long  as  there  is  any  sul- 
phuric acid  to  be  decomposed,  or  zinc  with  which  to  form 
zinc  sulphate. 

The  energy  which  previously  appeared  as  heat  only,  now 
appears  as  electric  energy. 

Therefore,  although  the  mere  contact  of  the  two  metals 
with  the  liquid  will  produce  a  difference  of  potential,  it  is  the 
chemical  potential  energy,  which  become  kinetic  during  the 
chemical  combination,  that  supplies  the  energy  required  to 
maintain  the  electric  current.  (See  Energy.  Kinetic  Po- 
tential. 

Simple  Voltaic  Cell. — A  simple  voltaic  cell  consists  of  two 


112  A  DICTIONARY  OF  ELECTRICAL 

plates  of  different  metals,  or  of  a  metal  and  a  metalloid  (or 
of  two  gases,  or  two  liquids,  or  of  a  liquid  and  a  gas),  each  of 
which  is  called  a  voltaic  element,  and  which,  taken  together, 
form  what  is  called  a  voltaic  couple. 

The  voltaic  couple  dips  into  a  liquid  called  an  electrolyte, 
which,  as  it  transmits  the  electric  current,  is  decomposed  by 
it.  The  elements  are  connected  outside  the  electrolyte  by  any 
conducting  material. 

Direction  of  the  Current. — In  any  voltaic  cell  the  current  is 
assumed  to  flow  through  the  liquid,  from  the  metal  most 
acted  on  to  the  metal  least  acted  on,  and  outside  the  liquid, 
through  the  ou'tside  circuit,  from  the  metal  least  acted  on  to 
the  metal  most  acted  on. 

In  Fig.  85,  a  zinc-copper  voltaic  couple 
is  shown,  immersed  in  dilute  sulphuric 
acid.  Here,  since  the  zinc  is  dissolved 
by  the  sulphuric  acid,  the  zinc  is  oosi- 
tive,  and  the  copper  negative  in  the  li- 
quid. The  zinc  and  copper  are  of  oppo- 
site polarities  out  of  the  liquid. 

It  will  of  course  be  understood  that  in 
the  above  sketch  the  current  flows  only 
on  the  completion  of  the  circuit  outside 
Fig.  85.  tne  C(?jj^  that  jg>  wnen  the  conductors  at- 

tached to  the  zinc  and  copper  plates  are  electrically  con- 
nected. 

Amalgamation  of  the  Zinc  Plate.— When  zinc  is  used  for 
the  positive  element,  it  will,  unless  chemically  pure,  be  dis- 
solved by  the  electrolyte  when  the  circuit  is  open,  or  will 
be  irregularly  dissolved  while  the  circuit  is  closed,  producing 
currents  in  little  closed  circuits  from  minute  voltaic  couples 
formed  by  the  zinc  and  such  impurities  as  carbon,  lead,  or  iron, 
etc.,  always  found  in  commercial  zinc.  (See,  Action,  Local.) 
As  it  is  practically  impossible  to  obtain  chemically  pure  zinc, 
it  is  necessary  to  amalgamate  the  zinc  plate,  that  is,  to  cover 


WORDS,  TERMS  AND  PHRASES.  113 

it  with  a  thin  layer  of  zinc  amalgam.  (See  Zinc,  Amalgama- 
tion of.) 

Polarization'  of  the  Negative  Plate. — Since  the  evolved  hy- 
drogen appears  at  the  surface  of  the  negative  plate,  after  a 
while  the  surface  of  this  plate,  unless  means  are  adopted  to 
avoid  it,  will  become  coated  with  a  film  of  hydrogen  gas,  or 
as  it  is  technically  called,  will  become  polarized.  (See  Polari- 
zation of  Voltaic  Cell.) 

The  effect  of  this  polarization  is  to  cause  a  falling  off  or 
weakening  of  the  current  produced  by  the  battery,  due  to  the 
formation  of  a  counter-electro-motive  force  produced  by  the 
hydrogen-covered  plate ;  that  is  to  say,  the  negative  plate, 
now  being  covered  with  hydrogen,  a  very  highly  electro-posi- 
tive element,  tends  to  produce  a  current  in  a  direction  opposed 
to  that  of  the  cell  proper.  (See  Counter-Electro-Motive  Force.) 

In  the  case  of  storage  cells,  this  counter-electro-motive  force 
is  employed  as  the  source  of  secondary  currents.  (See  Storage 
of  Electricity.  Storage  Cells.) 

In  order  to  avoid  the  effects  of  polarization  in  voltaic  cells, 
and  thus  ensure  constancy  of  current,  the  bubbles  of  gas  at  the 
negative  plate  are  mechanically  carried  off  either  by  roughen- 
ing its  surface,  by  forcing  the  electrolyte  against  the  plate  as  by 
shaking,  or  by  a  stream  of  air ;  or  else  the  negative  plate  is 
surrounded  by  some  liquid  which  will  remove  the  hydrogen, 
by  entering  into  combination  with  it.  (See  Polarization  of 
Voltaic  Cell.) 

Voltaic  cells  are  therefore  divided  into  cells  with  one  or  with 
two  fluids,  or  electrolytes,  or,  into 

(1)  Single-fluid  cells,  and 

(2)  Double-fluid  cells. 

Very  many  forms  of  voltaic  cells  have  been  devised.     The 
following  are  among  the  more  important,  viz.: 
SINGLE-FLUID  CELLS. 

The  Gre.net,  Poggendorff,  or  Bichromate  Cell— A  zinc-car- 
bon couple  used  with  an  electrolyte  known  as  electropoion,  a 


114 


A  DICTIONARY  OF  ELECTRICAL 


solution  of  bichromate  of  potash  and  sulphuric  acid  in  water. 
(See  Electropoion  Liquid.) 

The  zinc,  Fig.  86,  is  amalgamated  and  placed  between  two 
carbon  plates.  The  terminals  connected 
with  the  zinc  and  carbon  are  respect- 
ively negative  and  positive.  In  the 
form  shown  in  the  figure,  the  zinc  plate 
can  be  lifted  out  of  the  liquid  when  the 
cell  is  not  in  action. 

The  bichromate  cell  is  excellent  for  pur- 
poses requiring  strong  currents,  where 
long  action  is  not  necessary.  As  this  cell 
readily  polarizes,  it  cannot  be  advan- 
tageously employed  for  any  considerable 
period  of  time.  It  becomes  depolarized, 
however,  when  left  for  some  time  on 
open  circuit. 

The  following  chemical  reaction  takes 
place  when  the  cell  is  furnishing  cur- 
rent,  viz.: 

K!!Crj!0?-f7H!!S04-|-3Zn=K2S04-f3ZnS04+Cr23(S04)+7HgO. 
This  cell  gives  an  electro-motive  force  of  about  1.987  volts. 
The  Smee  Cell— A  zinc-silver  couple  used  with  an  electro- 
lyte of  dilute  sulphuric  acid,  HZSO4. 

The  silver  plate  is  covered  with  a  rough  coating  of  metallic 
platinum,  in  the  condition  known  as  platinum  black.  (See 
Platinum  Black.)  This  cell  was  formerly  extensively  em- 
ployed in  electro-metallurgy  but  it  is  now  replaced  by  dyna- 
mo-electric machines.  (See  Electro-Metallurgy.  Dynamo- 
Electric  Machine.) 

A  zinc-carbon  couple  is  sometimes  used  to  replace  the  zinc- 
silver  couple.  A  couple  of  zinc-lead  is  also  used,  though  not 
very  advantageously. 

The  Zinc-Copper  Cell. — A  zinc-copper  couple  used  with 
dilute  sulphuric  acid. 


'WORDS,  TERMS  AND  PHRASES. 


115 


This  was  one  of  the  earliest  forms  of  voltaic  cells. 

In  the  zinc-silver,  or  the  zinc-copper  couple,  the  chemical 
reaction  that  takes  place  when  the  cell  is  furnishing  current 
is  as  follows,  viz. : 

Zn  +  Ha  S04  —  Zn  SO4  +  H2. 

The  Smee  cell  gives  an  electro-motive  force  of  about .  65  volts. 
DOUBLE-FLUID  CELLS. 

Grove's  Cell. — A  zinc-platinum  couple  the  elements  of 
which  are  used  with  electrolytes  of  sulphuric  and  nitric  acids 
respectively. 

The  zinc,  Z,  Fig.  87,  is 
amalgamated  and  placed 
into  dilute  sulphuric  acid, 
and  the  platinum,  P,  into 
strong  nitric  acid  (H  NO3), 
placed  in  a  porous  cell  to 
separate  it  from  the  sul- 
phuric acid.  (See  Porous 
Cells.)  In  this  cell  the  cur- 
rent is  moderately  constant, 
since  the  polarization  of  the 
platinum  plate  is  prevented 
by  the  nitric  acid  that  oxy- 
dizes  and  thus  removes  the 
hydrogen  that  tends  to  be 
liberated  at  its  surface.  The 
constancy  of  the  current 
is  not  maintained  for  any  Fig.  87. 

considerable  time,  since  the  two  liquids  are  rapidly  decom- 
posed, or  consumed,  zinc  sulphate  forming  in  the  sulphuric 
acid,  and  water  in  the  nitric  acid. 

The  chemical  reactions  are  as  follows,  viz. : 
Zn  +  H8S04  =  Zn  SO4  +  H8; 
6H  4-  2H  NO,  =  4H20  +  2NO; 
3NO  +  08  =  N804. 


116 


A  DICTIONARY  OF  ELECTRICAL 


This  cell  gives  an  electro-motive  force  of  1.93  volts. 
Bunseri's    Cell. — A  zinc-carbon    couple,    the    elements    of 
which  are  immersed  respectively 
in  electrolytes  of  dilute  sulphuric 
and  strong  nitric  acids. 

Bunsen's  cell  is  the  same  as 
Grove's  except  that  the  platinum 
is  replaced  by  carbon.  The  zinc 
surrounds  the  porous  cell  contain- 
ing the  carbon.  The  polarity  is 
as  indicated  in  Fig.  88. 

The  Bunsencell  gives  an  electro- 
motive force  of  about  1.96  volts. 

DanlelTs   Cell.— A.   zinc-copper 
couple,    the   elements    of    which 
are  used  with  electrolytes  of  dilute 
sulphuric  acid,  and  saturated  so- 
lution of  copper  sulphate  respectively. 

The  copper  element  is  made  in  the  form  of  a  cylinder  c, 
Fig.  89,  and  is  placed  in  a 
porous  cell.  The  copper  cyl- 
inder is  provided  with  a  wire 
basket  near  the  top,  filled 
with  crystals  of  blue  vitriol, 
so  as  to  maintain  the  strength 
of  the  solution  while  the  cell 
is  in  use.  The  zinc  is  in  the 
shape  of  a  cylinder  and  is 
placed  so  as  to  surround  the 
porous  cell.  This  cell  gives  a 
nearly  constant  electro-mo- 
tive force. 

The  constancy  of  its  action 
depends  on  the  fact  that  for 
every  molecule  of  sulphuric  Fig.  89. 

acid  decomposed  in  the  outer  cell,   an  additional  molecule 


WORDS,  TERMS  AND  PHRASES. 


117 


Of  sulphuric  acid  is  supplied  by  the  decomposition  of  a  mole- 
cule of  copper  sulphate  in  the  inner  cell.     This  will  be  better 
understood  from  the  following  reactions  which  take  place,  viz. : 
Zn  +  H8  S04  =  Zn  SO4  +  H8 
H2  +  Cu  S04  =  H8  SO4  +  Cu. 

The  Ha  SO4,  thus  formed  in  the  inner  cell,  passes  through 
the  porous  cell,  and  the  copper  is  deposited  on  the  surface  of 
the  copper  plate. 

The  Daniell's  cell  gives  an  electro-motive  force  of  about 
1.072  volts. 

A  serious  objection  to  this  form  of  cell  arises  from  the  fact 
that  the  copper  is  gradually  deposited  over  the  surface  and  in 
the  pores  of  the  poi-ous  cell,  thus  greatly  varying  its  resistance. 
CallaucTs  Gravity  Cell. — A  zinc-copper  couple,  the  ele- 
ments of  which  are  em- 
ployed with  electrolytes  of 
dilute  sulphuric  acid,  or  di- 
lute zinc  sulphate,  and  a  con- 
centrated solution  of  cop- 
per sulphate  respectively. 
This  cell  was  devised  in 
order  to  avoid  the  use  of  a 
porous  cell.  As  its  name  in- 
d'icates,  the  two  fluids  are 
separated  from  each  other 
by  gravity. 

The  copper  plate  is  the 
lower  plate,  and  is  surround- 
ed by  crystals  of  copper  sul- 
phate. The  zinc,  generally 
in  the  form  of  an  open  wheel,  or  crowfoot,  is  suspended  near 
tlio  top  of  the  liquid,  as  shown  in  Fig.  90. 

The  reactions  are  the  same  as  in  the  Daniell  cell. 
A  dilute  solution  of  zinc  sulphate  is  generally  used  to  replace 
the  dilute  sulphuric  acid.     It  gives  a  somewhat  lower  electro- 
motive force,  but  ensures  a  greater  constancy  for  the  cell. 


Fig. 


A  DICTIONARY  6$  ELECTRICAL 


Fig.  91. 


The  Leclanche  Cell.— A  zinc-carbon  couple  the  elements  of 
which  are  used  with  a  solution  of  sal-ammoniac,  and  a  finely 
divided  layer  of  black-oxide  of  manganese  respectively. 

The  zinc  is  in  the  form  of  a  slender  rod  and  dips  into  a  sat- 
urated solution  of  sal-ammoniac,  NH4  Cl. 

The  negative  element  consists  of  a  plate  of  carbon,  C,  Fig. 

91,    placed    in    a 

Zn-   c&+Zn-        ^   Zn-         ^_     c      porous    cell,    in 

which  is  a  mix- 
ture of  black  ox- 
ide of  manganese 
and  broken  gas- 
retort  carbon, 
tightly  packed 
around  the  car- 
bon plate.  By 
this  means  a  greatly  extended  surface  of  carbon  surrounded 
by  black  oxide  of  manganese,  Mn  Oa,  is  secured.  The  entire 
outer  jar,  and  the  spaces  inside  the  porous  cell  are  filled  with 
the  solution  of  sal-ammoniac.  This  cell,  though  containing 
but  a  single  fluid,  belongs,  in  reality,  to  the  class  of  double- 
fluid  cells,  being  one  in  which  the  negative  element  is  sur- 
rounded by  an  oxidizable  substance,  the  black  oxide  of  man- 
ganese, which  replaces  the  nitric  acid,  or  copper  sulphate  in 
the  preceding  cell. 

The  reactions  are  as  follows,  viz.  : 

Zn  +  2  (NH4  Cl)  =  Zn  Cla  +  2NH8  +  H2. 
The  Zn  C18  and  NH8  react  as  follows  : 

Zn  Cl2-f2(NH8)  =  (2NH2)  Zn  Cla  +H8. 

2H  +  2(Mng  02)  =  H2  O  +  Mn2  O8, 
or,  possibly,  4H  +  3Mn  Oa  =  Mn3  O4  +  2H2  O. 
The  Leclanch6  cell  gives  an  electro-motive  force  of  about 
1.47  volts.     It  rapidly  polarizes,  and  cannot,  therefore,  give  a 
steady  current  for  any  prolonged  time.     When  left  on  open 
circuit,  however,  it  rapidly  depolarizes. 


WORDS,  TERMS  AND  PHRASES. 


119 


Of  all  the  voltaic  cells  that  have  been  devised  two  only, 
viz.,  the  Gravity  and  the  Leclanche,  have  continued  until 
now  in  veiy  general  use.  The  gravity  cell  being  used  on 
closed-circuit  lines  and  the  Leclanche  on  open-circuit  lines ; 
the  former  being  the  best  suited  of  all  cells  to  furnish  con- 
tinuous constant  currents  employed  in  most  systems  of  tele- 
graphy, and  the  latter  for  furnishing  the  intermittent  cur- 
rents required  for  ringing  bells,  operating  annunciators,  or  for 
similar  work. 

The  Siemens -Halske  Cell — 
A  zinc-copper  couple  the  ele- 
ments of  which  are  employed 
with  dilute  sulphuric  acid  and 
saturated  solution  of  copper  sul- 
phate respectively. 

This  cell  is  a  modification  of 
Daniell's.  A  ring  of  zinc,  Z  Z,  Fig. 
92,  surrounds  the  glass  cylinder 
c,  c.  The  porous  cell  is  replaced 
by  a  diaphragm,  /  /,  of  porous 
paper,  formed  by  the  action  of 
sulphuric  acid  on  a  mass  of  paper 
pulp.  Crystals  of  copper-sulphate 
are  placed  in  the  glass  jar,  c  c, 
and  rest  on  the  copper  plate  Jc, 
formed  of  a  close  copper  spiral. 
Terminals  are  attached  at  6  and 
h.  The  entire  cell  is  charged  with  dilute  sulphuric  acid. 
The  resistance  of  the  cell  is  high. 

The  Meidinger  Cell. — A  zinc-copper  couple  the  elements  of 
which  are  employed  with  dilute  sulphuric  acid,  or  solution  of 
sulphate  of  magnesia,  and  strong  nitric  acid,  respectively. 

This  is  another  modification  of  the  Daniell  cell.  The  zinc- 
copper  couple  is  thus  arranged  :  Z  Z,  Fig.  93,  is  an  amalga- 
mated zinc  ring  placed  near  the  walls  of  the  vessel,  A  A.  The 


130 


A  DICTIONARY  OF   ELECTRICAL 


copper  element  c  is  similarly  placed  with  respect  to  the  ves- 
sel  b  6.  The  glass  cylinder  h 
filled  with  crystals  of  copper  sul- 
phate, has  a  small  hole  in  its  bot- 
tom, and  keeps  the  vessel,  b  b, 
supplied  with  saturated  solution 
of  copper  sulphate.  The  cell  is 
charged  with  dilute  sulphuric  acid, 
or  a  dilute  solution  of  Epsom 
salts,  or  magnesium  sulphate. 
Cell,  Standard  Voltaic 

(See    Standard     Voltaic 

Cell.) 

Cements  Insulating 

— Various  mixtures  of  gums,  resins 
and  other  substances,  possessing 
the  ability  to  bind  two  or  more 
Fig.  93.  substances    together    and   yet   to 

electrically  insulate  one  from  the  other. 
Centi  (as  a  prefix).— The  one  hundredth  of. 
Centigrade    Thermometer  Scale.— A  thermometer 
scale  on  which  the  freezing  point  of  water  is  marked  0°,  and 
the  boiling  point  at  30  inches  of  the  barometer  100°. 

Centigrade  degrees  are  indicated  by  a  C.,  thus  0°  C.  or 
100°  C.,  to  distinguish  them  from  Fahrenheit  degrees  that  are 
marked  F.— (See  Thermometer.) 

Centigramme.— The  hundredth  of  a  gramme,  or  1544 
grains.  (See  Metric  System  of  Weights  and  Measures.) 

Centimetre.— A  length  equal  to  the  one  hundreth  of  a 
metre  or  .3937  inch.  (See  Metric  System  of  Weights  and 
Measures.) 

Centimetrc-Gramme-Second  System,  or  the  C. 
O.  S.  System. — A  system  of  units  of  measurement  in  which 
the  centimetre  is  adopted  for  the  unit  of  the  length,  the 


WORDS,  TERMS  AND  PHRASED.  121 

gramme  for  the  unit  of  mass,  and  the  second  for  the  unit  of 
time. 

This  is  the  same  as  the  Absolute  System  of  Units.  (See 
Absolute  Units.) 

Central  Station  Lighting.— (See  Lighting,  Central 
Station. 

Centre  of  Gravity.— (See  Gravity,  Centre  of  .) 

Centre  of  Oscillation.— (See  Oscillation,  Centre  of.) 

Centre  of  Percussion. — (See  Percussion,  Centre  of.) 

Centrifugal  Force  (so  called).— The  force  that  is  sup- 
posed to  urge  a  rotating  body  directly  away  from  the  centre 
of  rotation. 

If  a  stone  be  tied  to  a  string  and  whirled  around,  and  the 
string  break,  the  stone  will  not  fly  off  directly  away  from  the 
centre,  but  will  move  along  the  tangent  to  the  point  where  it 
was  when  the  string  broke. 

The  centrifugal  force  in  reality  is  the  force  which  is  repre- 
sented by  the  tension  to  which  the  string  is  subjected  during 
rotation. 

Centrifugal  Governor A  device  for  maintain- 
ing constant  the  speed  of  a  steam  engine  or  other  prime 
mover,  despite  sudden  changes  in  the  load,  or  work. 

In  a  ball  governor  any  increase  in  speed  causes  the  balls  to 
fly  out  from  the  centre  of  rotation  by  centrifugal  force,  which 
is  utilized  to  control  a  valve  or  other  regulating  device.  If 
the  speed  falls  the  balls  move  towards  the  centre,  shifting  the 
valve  or  regulating-  device  in  the  opposite  direction. 

Chain,  molecular (See  Molecular  Chain.) 

Chamber  of  Lamp.— The  glass  bulb  or  chamber  of  an 
incandescing  electric  lamp  in  which  the  incandescing  con- 
ductor is  placed,  and  which  is  generally  maintained  at  a  high 
vacuum. 

Characteristic  Curves.— Diagrams  in  which  curves  are 
employed  to  represent  the  ratio  of  certain  varying  values. 


122  A  DICTIONARY  OF  ELECTRICAL 

The  electro-motive  force  generated  in  the  armature  coils  of 
a  dynamo-electric  machine,  when  the  magnetic  field  is  of  a 
constant  intensity,  is  theoretically  proportional  to  the  speed 
of  rotation.  (In  practice  this  is  prevented  by  a  number  of  cir- 
cumstances). The  relation  existing  between  the  speed  and 
electro-motive  force  may  be  graphically  represented  by  refer- 
ring the  values  to  two  straight  lines,  one  horizontal  and  the 
other  vertical,  called  respectively  the 
axes  of  abscissas  and  ordinates. 
(See  Abscissas,  Axis  of.)  If,  in  a 
given  case,  the  number  of  revolutions 
are  marked  off  along  the  horizontal 
line  from  the  point  0,  Fig.  94,  in  dis- 
i*7  tances  from  0,  proportional  to  the 

Revolution*  i     <•  i    it, 

fig.  9i,.  number  of  revolutions,  and  the  cor- 

responding electro-motive  forces  are  marked  off  along  the 
vertical  line  in  distances  from  0,  proportional  to  the  electro- 
motive forces,  the  points  where  these  lines  intersect,  will 
form  the  characteristic  curve  as  shown  for  the  particular 
case. 

Charge,  Bound  and  Free (See  Bound  and 

Free  Charge.) 

Charge,  Density  of or  Electrical  Density.— 

The  quantity  of  electricity  at  any  point  on  a  charged  surface. 
Coulomb  used  the  phrase  Surface  Density  to   mean    the 
quantity  of  electricity  per  unit  of  area  at  any  point  on  a 
surface. 

Charge,  Electric The  quantity  of  electricity 

that  exists  on  the  surface  of  an  insulated  electrified  conductor. 

"When  such  a  conductor  is  touched  by  a  good  conductor  con- 
nected with  the  earth,  it  is  discharged. 

Charge,  Dissipation   of (See   Dissipation  of 

Charge.) 

Charge,   Distribution  of The  variations  that 


WORDS,  TERMS  AND  PHRASES.  123 

exist  in  the  density  of  an  electrical  charge  at  different  portions 
of  the  surface  of  all  insulated  conductors  except  spheres. 

The  density  of  charge  varies  at  different  points  of  the  sur- 
face of  conductors  of  various  shapes.  It  is  uniform  at  all 
points  on  the  surface  of  a  sphere. 

It  is  greatest  at  the  extremities  of  the  longer  axis  of  an  egg 
shaped  body,  and  greater  at  the  sharper  end. 

It  is  five  times  greater  at  the  corners  of  a  cube  than  at  the 
middle  of  a  side. 

It  is  greatest  round  the  edge  of  a  circular  disc. 

It  is  greatest  at  the  apex  of  a  cone. 

Charge,  Residual The  charge  possessed  by  a 

charged  Leyden  jar  a  few  moments  after  it  has  been  dis- 
i-uptively  discharged  by  the  connection  of  its  opposite  coatings. 

The  residual  charge  is  probably  due  to  a  species  of  dielectric 
strain,  or  a  strained  position  of  the  molecules  of  the  glass 
caused  by  the  charge.  Such  residual  charge  is  not  present  in 
air  condensers. 

Charge,  Return (See  Back  Stroke  or  Return.) 

Charging  Accumulators.— Sending  an  electric  current 
into  a  storage  battery  for  the  purpose  of  rendering  it  an  elec- 
tric source. 

There  is,  strictly  speaking,  no  accumulation  of  electricity 
in  a  storage  battery,  such  for  example  as  takes  place  in  a 
condenser.  (See  Storage  Batteries). 

Characteristics  of  Sound.— The  peculiarities  that 
enable  different  musical  sounds  to  be  distinguished  from  one 
another. 

The  characteristics  of  musical  sounds  are  : 

(1)  The  Tone  or  Pitch,  according  t    which  a  sound  is  either 
grave  or  shrill. 

(2)  The  Intensity  or  Loudness,  according  to  which  a  sound 
is  either  loud  or  feeble. 

(3)  The  Quality  or  Timbre,  the  peculiarity  which  enables  us 


124 


A  DICTIONARY  OF  ELECTRICAL 


to  distinguish  between  two  sounds  of  the  same  pitch  and 
intensity,  but  sounded  on  different  instruments,  as  for  example 
on  a  flute  and  on  a  piano. 

Chemical  Effect  or  Change.—  Such  a  change,  occa- 
sioned by  chemical  combination,  as  results  in  a  loss  of  thoca 
properties  or  peculiarities  by  which  the  substances  entering 
into  combination  are  ordinarily  recognized. 

Black  carbon,  and  yellow  sulphur,  for  example,  both  solids, 
unite  chemi.  .  .ly  to  form  a  transparent  colorless  liquid. 

Chemical  changes  differ  from  physical  changes,  which  latter 
can  occur  in  a  substance  without  the  loss  by  it  of  the  proper- 
ties it  ordinarily  possesses. 

Thus  a  sheet  of  vulcanite,  electrified  by  friction,  still  retains 
its  characteristic  density,  shape,  color,  etc. 

Chemical  Equivalent.  —  (See  Equivalent,  Chemical.) 
Chemical  Photometer.  —  (See  Photometers.) 

Chemical  Potential  Energy.  —  (See  Energy  Atomic, 
or  Energy  Potential.) 

Chemical  Recorder.  —  (See  Recorder,  Chemical,  Bain's.) 


Chimes,  Electric 


—  Bells, 


Fig.  95. 


rung  by  the  attractions  and  repul- 
sions of  electrostatic  charges. 

B  and  B,  Fig.  95,  are  directly  con- 
nected to  the  prime  or  positive 
conductor-)-,  of  a  frictional  machine. 
C  is  insulated  from  this  conductor 
by  means  of  a  silk  thread,  but  is  con- 
nected with  the  ground  by  the  me- 
tallic chain  C.  Under  these  circum- 
stances the  clappers,  /  I,  insulated 
by  silk  threads,  t  t,  are  attracted 
to  B,  B,  by  an  induced  charge  and 


repelled  to  C,  where  they  lose  their  charge  only  to  be  again 


WORDS,  TERMS  AND  PHRASES.  125 

attracted  to  B,  B.    In  this  way  the  bells  will  continue  ringing 
as  long  as  the  electric  machine  is  in  operation. 

Chronograph,  Electric  --  An  apparatus  for 
electrically  measuring  and  registering  small  intervals  of  time. 

Chronographs,  though  of  a  variety  of  forms,  generally  regis- 
ter minute  intervals  of  time  by  causing  a  tuning  fork  or  vibrat- 
ing bar  of  steel,  whose  rate  of  motion  is  accurately  known,  to 
trace  a  sinuous  line  on  a  smoke  blackened  sheet  of  paper, 
placed  on  a  cylinder  driven  by  clockwork,  at  a  uniform  rate 
of  motion.  If  a  fork  that  is  known  to  produce,  say,  256  vibra- 
tions per  second  be  used,  each  sinuous  line  will  represent  7£? 
part  of  a  second. 

An  electro-magnet  is  used  to  make  marks  on  the  line  at  the 
beginning  and  the  end  of  the  observation,  and  thus  permit  its 
duration  to  be  measured. 

Chronoscope,  Electric  —  —  An  apparatus  for  elec- 
trically indicating,  but  not  necessarily  recording,  small  inter- 
vals of  time. 

The  small  interval  of  time  required  for  a  rifle  ball  to  pass 
between  two  points  may  be  determined  by  causing  the  ball  to 
pierce  two  wire  screens  placed  a  known  distance  apart.  As 
the  screens  are  successively  pierced,  an  electric  circuit  is  thus 
made  or  broken,  and  marks  are  registered  electrically  on  any 
apparatus  moving  with  a  known  velocity. 

Circle,   Azimuth  --  (See 
Azimuth  Circle.) 

Circle,  Voltaic  or  Galvanic 
--  A  name  formerly  employed  || 


for  a  voltaic  cell  or  circuit. 

Circuit,  Astatic  ---  A  cir- 
cuit consisting  of  two  closed  curves 
enclosing  equal  surfaces. 

Such  a  circuit  is  not  under  the  action  of  the  earth's  field. 
The  circuit  disposed,  as  shown  in  Fig.  96,  is  astatic  and  pro- 


126  A  DICTIONARY  OF  ELECTRICAL 

duces  two  equal  and  opposite  fields  at  S  and  S'.  (See  Mag- 
netism, Ampere's  Theory  of.) 

Circuit,  Broken  or  Opened,  Made,  €lo§ed,  or 

Completed A  circuit  is  broken  or  opened,  when  its 

conducting  continuity  is  disturbed,  or  when  the  current  can- 
not pass. 

Circuit,  Closed,  Completed  or   made A 

circuit  is  closed,  completed,  or  made  when  its  conducting 
continuity  is  such  that  the  current  can  pass. 

Circuit,  Compound A  circuit  containing  more 

than  a  single  source,  or  more  than  a  single  electro-receptive 
device,  or  both,  connected  by  conducting  wires. 

The  term  compound  circuit  is  sometimes  applied  to  a  series 
circuit.  (See  Circuit,  Series.)  The  term,  however,  is  a  bad 
one,  and  is  not  generally  adopted. 

Circuit,  Earth- A  circuit  in  which  the  ground 

or  earth  forms  part  of  the  conducting  path.  (See  Circuit, 
Varieties  of.) 

Circuit,  Electric Literally  to  go  around. 

The  path  in  which  electricity  circulates  or  passes  from  a 
given  point,  around  or  through  a  conducting  path,  back  again 
to  its  starting  point. 

All  simple  circuits  consist  of  the  following  parts,  viz. : 

(1)  Of  an  electric  Source,  which  may  be  a  voltaic  battery 
a  thermo-pile,  a  dynamo-electric  machine,  or  any  other  means 
for  producing  electricity. 

(2)  Of  Leads  or  Conductors  for  carrying  the  electricity  out 
from  the  source,  through  whatever  apparatus  is  placed  in  the 
line,  and  back  again  to  the  source. 

(3)  Various  Electro-Receptive  Devices,  such  as  electro-mag- 
nets, electrolytic  baths,  electric  motors,  electric  heaters,  etc., 
through  which  the  current  passes  and  by  which  they  are  ac- 
tuated or  operated. 


WORDS,  TERMS  AND  PHRASES.  127 

Circuit,  External That  part  of  a  circuit  which  is 

external,  or  outside  the  electric  source. 

Circuit,    Grounded A  circuit    in    which    the 

ground  forms  part  of  the  path  through  which  the  current 
passes. 

As  the  ground  is  not  always  a  good  conductor,  the  terminals 
should  be  connected  with  the  gas  or  water  pipes,  or  with 
metallic  plates,  called  ground  plates.  Such  connection,  or 
any  similar  ground  connection  is  usually  termed  the  ground 
or  earth. 

Circuit  Indicator.— (See  Indicator.) 

Circuit,  Internal That  part  of  a  circuit  which  is 

included  within  the  electric  source. 

Circuit,  Line The  wire  or  other  conductors  in 

the  main  line  of  any  telegraphic  or  other  electric  circuit.     (See 
Circuits,  Varieties  of.) 

Circuit,  Liocal • — The  circuit  in  a  telegraphic  system 

in  which  is  placed  a  local  battery  as  distinguished  from  a  main 
battery.     (See  Telegraph,  Morse  System.) 

Circuit,  Ulain  Battery A  term  sometimes  used 

for  Line  Circuit.     (See  Circuit,  Line.) 

Circuit,  magnetic The  path  through  which  the 

lines  of   magnetic  force 
pass. 

All  lines  of  force  form 
closed  circuits. 

In  the  bar  magnet, 
shown  in  Fig.  97,  part  of 
this  path  is  through  the 
air.  In  order  to  reduce 
or  lower  the  resistance  Fig.  97 

of  a  magnetic  circuit,  iron  is  often  placed  around  the  mag- 
net.   The  magnet  is  then  said  to  be  iron-clad. 

The  armature  of  a  magnet  lowers  the  magnetic  resistance 


128  A  DICTIONARY   OF   ELECTRICAL 

by  affording  a  better  path  for  the  lines  of  magnetic  force  than 
the  air  between  the  poles. 

Circuit,  metallic —A  circuit  in  which  the  ground 

is  not  employed  as  any  part  of  the  path  of  the  current. 

Circuit,  Multiple-Series (See  Circuits,  Varie- 
ties of.) 

Circuit,  Parallel  or  multiple-Arc (See  Cir- 
cuits, Varieties  of.) 

Circuit,  Simple A  circuit  containing  a  single 

electric  source,'and  a  single  electro-receptive  device,  connected 
by  a  single  conductor. 

The  term  simple  circuit  is  sometimes  applied  to  a  multiple 
arc  circuit.  The  term  is  not,  however,  a  good  one,  and  is  not 
in  general  use. 

Circuit,  Serie§ (See  Circuits,  Varieties  of.) 

Circuit,  Series-Multiple (See  Circuits,  Varie- 
ties of.) 

Circuit,  Shunt    or    Derived A  circuit  which 

forms  an  additional  path  for  an  electric  current.  (See  Shunt, 
or  Derived  Circuit.) 

Circuits,  Varieties  of Conducting  paths  pro- 
vided for  the  passage  of  an  electric  current. 

Electric  circuits  may  be  divided  according  to  their  complex- 
ity into 

(1)  Simple. 

(2)  Compound. 

According  to  the  peculiarities  of  their  connections  into 

(1)  Shunt  or  Derived. 

(2)  Series. 

(3)  Parallel  or  Multiple- Arc. 

(4)  Multiple-Series. 

(5)  Series-Multiple. 


WORDS,  TERMS  AND  PHRASES.  129 

According  to  their  resistance  into 

(1)  High  Resistance. 

(2)  Low  Resistance. 

According  to  their  relation  to  the  electric  source  into 

(1)  Internal  circuits. 

(2)  External  circuits. 

According  to  their  position  in  the  circuit,  or  the  work 
done,  circuits  are  divided  into  very  numerous  classes;  thus  in 
telegraphy  we  have  the  following,  viz.  : 

(1)  The  Line  circuit. 

(2)  The  Earth  or  Ground  circuit. 

(3)  The  Local  Battery  circuit. 

(4)  The  Main  Battery  circuit,  etc. 

A  simple  circuit  is  one  which  contains  but  a  single  electric 
source  and  a  single  electro-receptive  device,  connected  by  a 
single  conducting  wire. 

A  compound  circuit  is  one  which  contains  more  than  a 
single  electric  source,  or  more  than  a  single  electro-receptive 
device,  or  both,  connected  by  conducting  wires. 

Either  the  circuits,  the  sources,  or  the  electro-receptive  de- 
vices may  be  connected  in  series,  in  multiple,  in  multiple-series, 
or  in  series-multiple. 

The  most  important  of  these  are  as  follows  : 

(1)  Series  circuits  or  connections.  Compound  circuits,  in 
which  the  separate  circuits,  or  sources,  are  connected  in  one 
line  by  joining  their  opposite  poles  so  that  the  current  pro- 
duced in  each  passes  successively  through  the  circuit. 


o* 

Fig.  98. 

The  six  cells,    shown  in  Fig.  98,  are  connected    in  series 
by  joining  the  positive  pole  of  each  cell  with  the  negative 


130 


A  DICTIONARY  OP  ELECTRICAL 


pole  of  the  succeeding  cell,  the  negative  and  positive  poles  at 
the  extreme  ends  being  connected  by  any  conductor. 

c  +  c+  CT+       „          The  connection 

of  three  Leclan- 
c!6  cells  in  series 
is  clearly  shown 
in  Fig.  99.  The 
carbons,  C  C,  of 
the  first  and  sec- 
ond cells  are  con- 
Fig.99.  nected  to  the 

zincs,  Zn  Zn,  of  the  second  and  third  cells,  thus  leaving  the 
zinc,  Zn,  of  the  first  cell,  and  the  carbon,  C,  of  the  third  cell, 
as  the  terminals  of  the  battery.  The  direction  of  the  current 
is  shown  by  the  arrows. 

The  resistance  of  such  a  connection  is  equal  to  the  sum  of 
the  resistances  of  each  of  the  separate  sources. 

The  electro-motive  force  is  equal  to  the  sum  of  the  separate 
electro-motive  forces. 

If  the  electro-motive  force  of  a  single  cell  is  equal  to  E,  its 
internal  resistance  to  r,  and  the  resistance  of  the  leads  and 
electro-receptive  devices  to  r',  then  the  current  in  the  circuit, 


s~i 


E 


r  +  r' 

If  six  of  such  cells  are  coupled  in  series,  the  current  becomes 
6E 

/I  ^ 

~ 


If,  however,  the  internal  resistance  of  each  cell  be  so  small 
as  to  be  neglected,  the  formula  becomes 

6E 
C-*  — ; 

r' 

or  the  current  is  six  times  as  great  as  with  one  cell. 


WORDS,  TERMS  AND  PHRASES. 


131 


The  series  connection  of  battery  cells  is  used  on  telegraph 
lines,  or  in  all  cases  where  a  high  electro-motive  force  is  re- 
quired in  order  to  overcome  a  considerable  resistance  in  the 
circuit.  The  instruments  are  also  generally  connected  to  the 
line  in  series. 

This  series  connection  was  formerly  called  Connection  for 
Intensity.     The  term  is  now  abandoned. 
C 


Fig.  100. 

(2)  Parallel  Circuit,  or  Multiple-Arc. — A  compound  circuit 
ill  which  the  separate  sources,  or  the  separate  electro-receptive 
devices,  or  both,  are  connected  by  one  set  of  terminals,  such 
as  the  positive,  to  one  lead,  or  main  positive  conductor;  and 
all  the  negative  terminals  are  similarly  connected  to  another 
lead,  or  main  negative  conductor,  as  shown  in  Fig.  100. 


Fig.  101. 

The  connection  of  three  Bunsen  cells,  in  multiple-arc,  is 
shown  in  Fig.  101,  where  the  three  carbons,  C  C  C,  are  con- 


132  A  DICTIONARY  OF  ELECTRICAL 

nected  together  to  form  the  positive,  or  -f-  terminal  of  the 
battery,  and  the  three  zincs,  Zw  Zn  Zn,  are  similarly  connected 
tog-ether  to  form  the  negative,  or  —  terminal. 

The  electro-motive  force  is  the  same  as  that  of  a  single  cell, 
or  source.  The  internal  resistance  of  the  source  is  as  much 
less  than  the  resistance  of  any  single  source  as  the  area  of 
the  combined  negative  or  positive  plates  is  greater  than  that 
of  any  single  negative  or  positive  plate  ;  or,  in  other  words,  is 
less  in  proportion  to  the  number  of  cells,  or  other  separate 
sources  so  coupled. 

In  the  case  of  the  six  cells  above  referred  to,  the  current 
would  be, 

E 


C  =  r 

i+r' 

where  E,  is  the  electro-motive  force,  r,  the  internal  and  r1, 
the  external  resistance. 

The  effect  of  multiple  connection  on  the  internal  resistance 
of  the  source  is  to  increase  the  area  of  cross  section  of  the 
liquid  in  the  direct  proportion  of  the  number  of  cells  added. 
.     .. C 


Fig.  102. 

When  strong  or  large  currents  of  low  electro-motive  force  are 
required,  connections  in  multiple-arc  are  generally  employed. 

The  multiple-arc  connection  was  formerly  called  the  Con- 
nection for  Quantity.  This  term  is  now  abandoned. 


WORDS,  TEEMS  AND  PHRASES. 


133 


(3)  Multiple-Series  Circuit.  —  A  compound  circuit  in  which 
the  separate  sources,  or  electro-receptive  devices,  are  con- 
nected in  groups  in  multiple-  arc,  and  the  members  of  each 
group  subsequently  connected  in  series. 

In  Figs.  102  and  103,  multiple-series  circuits  of  six  sources 
are  shown.     The   '• 
current  takes  the 
paths  indicated 
by    the    arrows. 
The  electro-mo- 
tive force  of  the 
source  will  be  in- 
creased   in    pro-     ^^^_ 
portion  to   the  Fig.  103. 

number  of  cells  in  series,  and  the  internal  resistance  decreased 
in  proportion  to  the  number  in  parallel.  Supposing  the  circuit 
closed  by  a  resistance  equal  to  r',  the  current  would  be,  in 
Fig.  102, 

2E 


J 


C=    2r 


and  that  in  the  Fig.  103, 


(4)  In  Series- Multiple;  the  method  adopted  in  the  use  of  dis- 
tribution boxes,  a  number  of  multiple  groups  or  circuits  are 


*^     .  * 

Fig.  10k. 

connected  with  each  other  in  series,  as  shown  in  Fig.   104. 
(See  Box,  Distribution,  for  Arc  Light  Circuits.) 


134  A  DICTIONARY  OF  ELECTRICAL 

In  this  connection  the  resistance  of  each  multiple  group  is 
equal  to  the  resistance  of  a  single  branch  divided  by  the  num- 
ber of  branches. 

The  total  resistance  of  the  circuit  is  equal  to  the  sum  of  the 
resistances  of  the  multiple  groups. 

The  resistances  of  the  separate  compound  circuits  is  as  fol- 
lows :  Calling  R',  R",  and  R'",  the  resistance  of  each  of  the 
separate  parts  and  the  joint  resistance  R. 

(1)  For  the  series  circuit, 

R  =  R'  +  R"  +  R'". 

(2)  For  the  parallel  circuit, 

R'XR"XR'" 
R'R"+R"R'"  +  R'R'"  ; 

or,  what  is  the  same  thing,  the  conductivity  of  a  multiple  cir- 
cuit is  the  sum  of  the  reciprocals  of  the  separate  resistances; 
1          1          1 

or,  Conductivity  = 1 1 . 

R'        R"       R'" 

(3)  For  the  multiple-series  circuit,  if  the  resistance  of  each 
circuit  is  r,  then  the  total  resistance 

2r 
E=_, 

when  three  are  in  parallel  and  two  in  series  ;  and 

3r 
R=  —    , 

2      '        . 
when  two  are  in  parallel  and  three  in  series. 

(4)  For  the  series-multiple  circuit,  calling  r  the  resistance 
of  each  separate  circuit  in  the   five   parallel   circuits,   then 
the  resistance  of  each  of  the  parallel  groups  is 

r 
R=  — ; 

5 

and  the  total  resistance  of  the  three  groups  is 
r       r       r  3r 

R=-H h-    =   -• 

555  5 


WORDS,  TERMS  AND  PHRASES.  J85 

Circular  Uilit§. — Units  based  upon  the  value  of  the  area 
of  a  circle  whose  diameter  is  unity. 
Circular  Units  (Cross-Sections),  Table  of. 

1  circular  mil =    .78540  square  mil. 

"  =    .00064514  circular  millimetre. 

"  =    .00050669  square  millimetre. 

1  square   mil =  1.2732  circular  mils. 

=    .00082141  circular  millimetre. 

1  circular  millimetre =  1550.1  circular  mils. 

=  1217.4  square  mils. 

.  =    .  78540  square  millimetre. 

1  square  millimetre =  1973.6  circular  mils. 

' '  - =  1 .2732  circular  mi llimetres. 

If  d  is  the  diameter  of  a  circle,  the  area  in  other  units  is  • 
If  d  is  in  mils.,  area  in  sq. 

millimetres =  d2  x    .00050669. 

d  in  millimetres,  area  in  sq. 

mils... -ds  x  1217.4. 

d  in  centimetres,  area  in  sq. 

inches =  d8  x  12174. 

d  in  inches,  area  in  sq.  centi- 
metres   =  d*  x  5.0669. 

(Hering.) 

Clamp  or  Clutch  for  Arc  Lamps.— A  clamp  for 
gripping  the  lamp-rod,  i.  e.,  the  rod  that  supports  the  carbon 
electrodes  of  arc  lamps.  (See  Lamp,  Electric  Arc.) 

Cleats. — Insulating  supports  for  attaching  wires  to  the 
walls  or  ceilings  of  buildings. 

Clepsydra,  Electric An  instrument  for  measur- 
ing time  by  the  escape  of  water  or  other  liquid  under  electrical 
control. 

Clocks,  Electric Clocks,  the  works  of  which  are 

moved  either  entirely  or  partially  by  the  electric  current, 
are  controlled  or  regulated  by  the  electric  current,  or  nre 
wound  thereby. 


136 


A  DICTIONARY  OF  ELECTRICAL 


Electric  clocks  may  therefore  be  divided  into  three  classes, 
viz.  : 

(1)  Those  in  which  the  works  are  moved  entirely  or  partially 
by  the  electric  current. 

(2)  Those  which  are  controlled  or  regulated  by  the  electric 
current. 

(3)  Those  which  are  merely  wound  by  the  current. 

A  clock  moving  independently  of  electric  power,  is  given  a 
slight  retardation  or  acceleration  electrically  and  is  thus  pre- 
vented from  gaining  or  losing  time.  The  entire  motion  of 
the  balance  wheel  is  sometimes  imparted  by  electricity. 

An  example  of  one  of  many  forms  of  electric  clock  is  shown 
in  Fig.  105,  where  the  split  battery  (See  Battery,  Split),  P  N,  is 
connected,  as  shown,  to  the  spring  contacts  S  and  S'. 


W 


Fig.  105. 

By  these  means  currents  are  sent  into  the  circuit  in  alter- 
nately opposite  directions.  The  pendulum  bob,  Fig.  106,  of  the 
controlled  clock  is  formed  of  a  hollow  coil  of  insulated  wire, 
which  encircles  one  or  both  of  two  permanent  magnets, 


WORDS,  TERMS  AND  PHRASES. 


137 


A  and  A',  placed  with  their  opposite  poles  facing  each  other. 
In  this  manner  a  slight  motion  forwards  or  backwards  is  im- 
parted to  the  pendulum  which  is  thus  kept  in  time  with  the 
controlling  clock. 

The  controlling  clock  is  shown  in  Fig.  105,  and  the  controlled 
clock  in  Fig.  106.  Mercury  contacts  are  sometimes  employed 
in  place  of  the  springs  S  and  S'.  Induction  currents  may  also 
be  employed. 

Clocks  of  non-electric  action  may  be  electrically  controlled, 
or  correctly  set  at  certain  intervals,  either  automatically  by  a 
central  clock,  or  by  the  depression  of  a  key  operated  by  hand 
from  an  astronomical  observatory. 

In  a  system  of  Time  Telegraphy,  the  controlling  clock  is 
called  the  Master  Clock,  and  the  controlled  clocks  the  Second- 
ary Clocks. 

Secondary  clocks  are  generally  mere  dials,  containing  step- 
by-step  movements,  for  moving  the  hour,  minute  and  second 
hands.  (See  Telegraphy,  Step-by-Step.) 


Fig.  107. 

In  Spellier's  clock,  a    series  of    armatures    H,    Fig.    107, 
mounted  on  the  circumference  of  a  wheel,  connected  with  the 


138  A  DICTIONARY  OF  ELECTRICAL 

escapement  wheel,  pass  successively,  with  a  step-by -step  move- 
ment, over  the  poles  of  electro-magnets.  On  the  completion 
of  the  circuit,  they  are  attracted  towards  the  magnet,  and  on 
the  breaking  of  the  circuit  they  are  drawn  away  by  the  fall  of 
the  weight  F,  placed  on  the  lever  D,  pivoted  at  E.  A  pulley 
at  E,  runs  over  the  surface  of  a  peculiarly  shaped  cog  on  the 
escapement  wheel. 

Clock,  Electric  Annunciator A  clock,  the 

hands  or  works  of  which,  at  certain  predetermined  times, 
make  electric  contacts  and  thus  ring  bells,  release  drops,  trace 
records,  etc.  ' 

Clock,  master The  controlling  clock  used  in  a 

system  of  time  telegraphy.  (See  Clocks,  Electric.) 

Clock-work  Feed  for  Arc  Lamps.— Arrangements 
of  clock-work  for  obtaining  a  uniform  feed  motion  of  one  or 
both  electrodes  of  an  arc  lamp. 

The  clock-work  is  automatically  thrown  into  or  out  of  action 
by  an  electro-magnet,  usually  placed  in  a  shunt  circuit  around 
the  carbons. 

Clocks,  Secondary The  clocks  in  a  system  of 

time  telegraphy  that  are  controlled  by  the  master  clock. 
(See  Clocks,  Electric.) 

Clocks,  Self- Winding Clocks  that  at  regular 

intervals  are  automatically  wound  by  the  action  of  a  small 
electro-magnetic  motor  contained  in  the  clock. 

Closed  Circuit.— (See  Circuit,  Closed,  Completed  or 
Made.) 

Closure.— The  completion  of  an  electric  circuit. 

Coatings,  Condenser The  sheets  of  tin  foil  on 

opposite  sides  of  a  Leyden  Jar  or  condenser,  which  receive  the 
opposite  charges. 

Coatings,  metallic Coverings  or  coatings  of 

metals,  deposited  from  solutions  of  metallic  salts  by  the  action 
of  an  electric  current.  (See  Electro-Plating.) 


WORDS,  TERMS  AND  PHRASES.  139 

Code,  Cipher  ---  A  code  in  which  a  number  of  words 
or  phrases  are  represented  by  single  words. 

The  message  thus  received  requires  the  possession  of  the 
key  to  render  it  intelligible. 

Code,  Telegraphic  —  -  —The  pre-arranged  signals  of 
any  system  of  telegraphy.  (See  Alphabet,  Telegraphic;  Morse, 
Continental.) 

Coefficient,  Algebraic  ---  A  number  prefixed  to 
any  quantity  to  indicate  how  many  times  that  quantity  is  to 
be  taken. 

The  number  3,  in  the  expression  3a,  is  a  coefficient  and  in- 
dicates that  the  a,  is  to  be  taken  three  times,  as  a  -\-a-{-a  —  3a. 

Coefficient,  Economic  --  of  a  Dynamo 
Electric  Machine.—  The  ratio  between  the  electrical  en- 
ergy or  the  electrical  horse  power  developed  by  the  current 
produced  by  a  dynamo,  and  the  mechanical  horse  power  ex- 
pended in  driving  the  dynamo. 

The  Efficiency  may  be  the  Commercial  Efficiency,  which  is 
the  useful  or  available  energy  in  the  external  circuit  divided 
by  the  total  mechanical  energy  ;  or  it  may  be  the  Electrical 
Efficiency,  which  is  the  available  electrical  energy  divided  by 
the  total  electrical  energy. 

The  Efficiency  of  Conversions  the  total  electrical  energy 
developed,  divided  by  the  total  mechanical  energy  applied. 

If  M,  equals  the  mechanical  energy, 

W,  the  useful  or  available  electrical  energy,  and 
w,  the  electrical  energy  absorbed  by  the  machine,  and 
m,  the  Stray  Power,  or  the  power  lost  in  friction,  eddy 
currents,  air  friction,  etc.     Then,  since 

M  =  W+to-fm, 

W  W 

Commercial  Efficiency-.  =          —  =  —  -- 

M       W  -J-  iv  -j-  m 

Electrical  Efficiency  ....  = 


.hmciency  of  Conversion 

M 


W  4-  w  W  4-  w 

-  •  —  =  -  '  -- 


140  A  DICTIONARY  OF  ELECTRICAL 

Coefficient,  Economic (See  Economic  Coeffi- 
cient.) 

Coefficient  of  magnetization,  or  Coefficient  of 
magnetic  Induction.— A  number  representing  the  inten- 
sity of  magnetization  produced  in  a  magnetizable  body  as 
compared  with  the  intensity  of  magnetization  of  the  induc- 
ing body. 

A  magnetizable  body,  when  placed  in  a  magnetic  field,  con- 
centrates the  lines  of  magnetic  force  on  it,  or  causes  them  to 
run  through  it.  The  intensity  of  the  magnetization  so  pro- 
duced depends,  therefore, 

(1)  On  the  intensity  of  the  magnetizing  field. 

(2)  On  the  ability  of  the  metal  to  concentrate  the  lines  of 
force  on  it,  that  is,  on  the  nature  of  the  metal,  or,  on  its  mag- 
netic permeability.    (See  Magnetic  Permeability.) 

The  intensity  of  magnetization  will  therefore  be  equal  to 
the  product  of  the  coefficient  of  magnetization,  and  the  in- 
tensity of  the  magnetizing  field. 

The  coefficient  of  magnetization  of  paramagnetic  bodies  is 
said  to  be  positive ;  that  of  diamagnetic  bodies  to  be  negative 
because  the  former  concentrate  the  lines  of  magnetic  force  on 
them,  and  the  latter  appear  to  repel  them.  (See  Paramag- 
netic. Diamagnetic.) 

Coefficient  of  mutual  Induction.— A  quantity  rep- 
resenting the  relative  number  of  lines  of  magnetic  force 
which  each  of  two  neighboring  electric  circuits  induce  in  the 
other. 

Coefflcient§  of  Expansion.— The  fractional  increase 
in  its  dimensions  of  a  bar  or  rod  when  heated  from  32°  to 
33°  F.,  or  from  0°  to  1°  C. 

The  fractional  increase  in  its  length  is  called  the  Coefficient 
of  Linear  Expansion. 

The  fractional  increase  in  its  surface  is  called  the  Coefficient 
of  Surface  Expansion, 


WORDS,  TERMS  AND  PHRASfiS.  141 

The  fractional  increase  in  its  volume  is  called  the    Coeffi- 
cient of  Cubic  Expansion. 
Coefficients  of*  Linear  Expansion.— 

Gold 0.000015153 

Steel ., 0.000010972 

Silver 0.000019086 

Copper 0.000017173 

Brass 0.000018782 

Tin 0.000019376 

Iron 0.000012350 

Flint  glass 0.000008116 

Platinum 0.000009918 

Lead... 0.000088483 

Zinc 0.000029416 

(Laplace  and  Lavoisier). 

Coercive,  or  Coercitive  Force.— The  power  of  resist- 
ing magnetization  or  demagnetization. 

Coercive  Force  is  sometimes  called  Magnetic  Retentivity. 
Hardened  steel  possesses  great  coercive  force ;  that  is,  it  is 
magnetized  or  demagnetized  with  difficult}'. 
Soft  iron  possesses  very  feeble  coercive  force. 
It  is  on  account  of  the  feeble  coercive  force  of  the  soft  iron 
core  of  an  electro-magnet  that  its  main  value  depends,  since 
it  is  thereby  enabled  to  rapidly  acquire  its  magnetization,  on 
the  completion  of  a  battery  circuit  through  its  coils,  and  to 
rapidly  lose  its  magnetization,  on  the  opening  of  the  circuit. 

Coils,    Armature (See   Dynamo-Electric   Ma- 
chines, Armature  Coils.) 

Coils,  Electric Convolutions  of  insulated  wire 

through  which  an  electric  current  may  be  passed.     (See  Elec- 
tro-Magnet. 

Coils,  Henry's A  number  of  separate  induction 

coils  so  connected  that  the  currents  induced  in  the  secondary 
wire  of  the  first  coil  are  caused  to  induce  currents  in  the 


143 


A  DICTIONARY  OF  ELECTRICAL 


secondary  wire  of  the  second  coil,  with  whose  primary  it  is 
connected  in  series. 

A  series  of  three  of  Henry's  coils  is  shown  in  Fig.  108. 
An  intermittent  battery  current  is  sent  into  a,  the  secondary 
of  which,  b,  is  connected  with  the  primary  c,  of  the  second 
coil.  The  secondary  d,  of  the  second  coil,  is  connected  with 
the  primary  e,  of  the  third  coil,  and  the  currents  finally  in- 
duced in  /,  are  employed  for  any  useful  purpose,  such  as  the 
magnetization  of  a  bar  of  iron  at  g. 


Fig.  108. 


fig.  109. 

The  current  in  b  is  sometimes  called  a  Secondary  Current; 
that  induced  by  this  secondai-y  current  in  d  is  called  a  Ter- 
tiary Current,  or  a  Current  of  the  Third  Order;  that  in/,  a 
Current  of  the  Fourth  Order.  Henry  carried  these  successive 
inductions  up  to  currents  of  the  Seventh  Order. 

Henry's  coils  in  realitj'  consist  of  separate  induction  coils, 
connected,  as  above  explained,  in  series. 

In  Fig.  109,  the  tertiary  current  induced  in  IV.,  may  be 
employed  to  give  shocks  to  a  person  grasping  the  handles, 
e  and/. 


WORDS,  TERMS  AND  PHRASES. 


143 


—  (See  Induction  Coils.) 


—  (See  Magnet  Coils.) 
Coils  of  wire,  the  electrical 


Fig.  110. 


Coils  Induction  - 
4 'oil-.  Magnet  — 
Coils,  Resistance 

resistance  of  which  is  known,  employed  for  measuring  the  re- 
sistance of  any  circuit. 

In  order  to  avoid  the  mag- 
netizing effects  of  the  coils  on 
the  needles  of  the  galvanome- 
ters used  in  electric  measure- 
ments, the  wire  of  the  re- 
sistance coil  is  doubled  on 
itself  before  being  wound, 
and  its  ends  electrically  con- 
nected with  the  brass,  bars, 
E,  E,  Fig.  110.  The  insertion 
of  the  plug-key  cuts  the  coil 
out  of  the  circuit  by  short- 
circuiting.  (See  Box,  Resistance.  Balance,  Wheat  stone's, 
Electric.  Standard  Resistance  Coil.) 

The  coils  are  made  of  German  silver,  or  platinoid,  whose 
resistance  is  not  much  affected  by  heat. 

Coils,  Shunt Coils  placed  in  a  derived  or  shunt 

circuit.     (See  Circuit,  Shunt.) 

Collectors  of  Dynamo  Electric  machines.— The 
metallic  brushes  that  rest  on  the  commutator  cylinder,  and 
carry  off  the  current  generated  on  the  rotation  of  the  arma- 
ture. Collectors  are  familiarly  called  commutators. 

Collectors,  Electric.— Devices  employed  to  collect  or 
take  off  electricity  from  a  moving  electric  source. 

Collectors  of  Frictioiial  Electrie  Machines.— 
The  metallic  points  that  collect  the  charge  from  the  glass  plate 
or  cylinder  of  a  frictional  electric  machine. 

Column,  Electric A  term  formerly  applied  to  a 

voltaic  pile.     (See  Pile,  Voltaic.) 


144  A  DICTIONARY  OF  ELECTRICAL 

Completed  Circuit.— (See  Circuit,  Closed,  Completed  or 
Made.) 

Commercial  Efficiency  of  Dynamo.— The  useful  or 
available  electrical  energy  in  the  external  circuit,  divided  by 
the  total  mechanical  energy  required  to  drive  the  dynamo 
that  produced  it.  (See  Coefficient,  Economic,  of  Dynamo.) 

Commutator.— Generally,  a  device  for  changing  the  di- 
rection of  an  electric  current. 

That  part  of  a  dynamo-electric  machine  that  causes  the  cur- 
rents that  alternate  or  change  their  direction  twice  in  every 
revolution  of  the  armature,  between  a  pair  of  magnet  poles, 
to  flow  in  one  and  the  same  direction  in  the  external  circuit. 

One  end  of  an  armature  coil  is  connected 
with  A',  Fig.  Ill,  and  the  other  with  A. 
The  brushes  are  so  set  that  A  and  A'  are 
in  contact  with  B'  and  B,  respectively,  as 
long  as  the  current  flows  in  the  same 
direction,  in  the  armature  coil  connected 
therewith,  but  enter  into  contact  with  B 
and  B',  when  the  current  changes  its  di- 
Fig.  ill.  rection,  and  continue  in  such  conjtact  as 

long  as  it  flows  in  this  direction.  The  current  ivill  therefore 
flow  through  any  circuit  connected  with  the  brushes  in  one 
and  the  same  constant  direction. 

The  number  of  metallic  pieces  A  and  A',  in  the  commutator 
cylinder  depends  on  the  number,  arrangement  and  con- 
nection of  the  armature  coils,  and  on  the  disposition  of  the 
magnetic  field  of  the  machine. 

For  details  of  various  commutators  of  this  description,  see 
Dynamo-Electric  Machines. 

The  Reverser  used  by  Ruhmkorff  in  his  induction  coil,  for 
cutting  off,  or  for  reversing  the  direction  of  the  primary  current 
is  shown  in  Fig.  112,  and  was  called  by  him  the  commutator. 
(See  Ruhmkorff  Coil.) 

Two  metallic  strips,  V  V,  supported  on  a  cylinder  of  insu- 


WORDS,  TERMS  AND  PHRASES. 


145 


lating  material  are  in  contact  with  the  battery  terminals  P 
and  N  through  two  vertical  springs  that  bear  on  them.  On  a 
half  rotation  of  the  cylinder  by  the  thumb  screw  L,  the  strips 
V,  V,  change  places  as  regards  the  vertical  springs,  and  thus 
reverse  the  direction  of  the  battery  current. 


Fig.  113. 


Compass,  \ximul li.  or  llariner'§- 


— A  compass 


used  by  mariners  for  measuring  the  hoi'izontal  distance  of  the 
sun  or  stars  from  the  magnetic  meridian.  (See  Azimuth, 
Magnetic.) 

A  single  magnetic  needle,  or  several  magnetic  needles,  are 
placed  side  by  side  on  the  lower  surface  of  a  card,  called  the 
compass  card.  This  card  is  divided  into  the  four  cardinal 
jtoints,  N,  S,  E  and  W,  and  these  again  sub-divided  in  thirty- 
two  points  called  Rhumbs. 

In  the  azimuth  compass  these  divisions  are  supplemented 
by  a  further  division  into  degrees. 


146 


A  DICTIONARY  OF  ELECTRICAL 


A  form  of  azimuth  compass  is  shown  in  Fig.  113.  In  order 
to  maintain  the  compass  box  in  a  horizontal  position,  despite 
the  rolling  of  the  ship,  the  box,  A  B,  is  suspended  in 
the  larger  box,  P  Q,  on  two  concentric  metallic  circles,  C  D, 

and  E  F,  pivoted  on 
two  horizontal  axes 
at  right  angles  to 
each  other ;  or,  as  it 
is  technically  term- 
ed, in  O  i  m  b  a  I  s . 
Sights,  G  H,  are 
provided  for  meas- 
uring the  magnetic 
azimuth  of  any  ob- 
ject. 

€ompa§§Card. 

— (See  Compass,  Az- 
mff.  118.  imuth.) 

Compensating  Magnet.— (See  Magnet,  Compensating.) 

Component,  Horizontal  and  Ver- 
tical,   of    Earth's   Magnetism.— That 

portion  of  the  earth's  directive  force  which 
acts  in  a  horizontal  direction. 

Let  A  B,  Fig.  114,  represent  the  direction 
and  magnitude  of  the  earth's  magnetic  field 
on  a  magnetic  needle.  The  magnetic  force 
will  lie  in  the  plane  of  the  magnetic  meridian, 
which  will  be  assumed  to  be  the  plane  of  the 
paper  CAD.  The  earth's  field,  A  B,  can  be 
resolved  into  two  components,  A  D,  the  hori- 
zontal component,  and  A  C,  the  vertical  ^ 
component. 

In  the  case  of  a  magnetic  needle,  which,  like  the  ordinary 
compass  needle,  is  free  to  move  in  a  horizontal  plane  only,  the. 


WORDS,  TERMS  AND  PHRASES.  147 

horizontal  component  alone  directs  the  needle.  When  the 
noodle  is  free  to  move  in  a  vertical  plane,  and  the  plane  cor 
responds  with  that  of  the  magnetic  meridian,  this  entire  mag- 
n olio  force,  A  B,  acts  to  place  the  needle,  supposed  to  be 
properly  halanced,  in  the  direction  of  the  lines  of  force  of  the 
earth's  magnetic  field  at  that  point.  In  the  vertical  plane  at 
right  angles  to  the  plane  of  the  magnetic  meridian,  the  ver- 
tical component  alone  acts,  and  the  needle  points  vertically 
downwards. 

Components. — The  two  or  more  separate  forces  into 
which  any  single  force  may  be  resolved  ;  or,  conversely,  the 
separate  forces  which  together  produce  any  single  resulting 
force. 

When  two  or  more  forces  simultaneously  act  to  produce 
motion  in  a  body,  the  body  will  move  with  a  given  force  in  a 
single  direction  called  the  resultant.  The  separate  forces,  or 
directions  of  motion,  are  called  the  components. 

Two  forces  acting  simultaneously  on  a  body  at  A,  Fig.  115, 
tending  to  move  it  in  the  direction  of  the  arrows,  along  A  B 
and  A  C,  with  intensi- 
ties proportioned  to  the 
lengths  of  the  lines  A  B 
and  A  C,  respectively, 
will  move  it  in  the  direc- 
tion A  D,  obtained  by 
drawing  B  D  and  D  C, 
parallel  to  A  C  and  A  B, 
respectively,  and  draw-  Fig.  115. 

ing  A  D  through  the  point  of  intersection,  D.  This  is  called 
the  Composition  of  Forces.  A  D  is  the  resultant  force  and 
A  B  and  A  C  are  its  components. 

Conversely,  a  single  force,  acting  in  the  direction  of  D  B, 
Fig.  116,  against  a  surface,  B  C,  may  be  regarded  as  the 
resultant  of  the  two  separate  forces,  D  E  and  D  C,  one  parallel 
to  C  B,  and  one  perpendicular  to  it  D  E,  being  parallel  to 


148  A  DICTIONARY  OF  ELECTRICAL 

C  B,  produces  no  pressure,  and  the  absolute  effect  of  the  force 

will  be    represented    by 
C  D. 

This  is  called  the  reso- 
lution of  forces,  the  force, 
D  B,  being  resolved  into 
the  components  D  E  and 
DC. 

Tluit  component  of  the 

fig.  no.  earth's    magnetic    force 

which  acts  in  a'horizontal,or  in  a  vertical  direction  respectively. 
Compound,    Binary Compound,    Chatter- 
ton's. — A  compound  for  cementing  together  the  alternate 
coatings  of  gutta-percha  employed  on  a  cable  conductor,  or 
for  filling  up  the  spaces  between  the  strand  conductors.     (See 
Binary  Compound.) 
The  composition  is  as  follows  : 

Stockholm  tar 1  part  by  weight. 

Resin 1  " 

Gutta-percha- 3  " 

(Clark  &  Sdbine.) 

Compound,  Clark's. — A  compound  for  the  outer  casing 
of  the  sheath  of  submarine  cables. 
Its  composition  is  as  follows  : 

Mineral  pitch 65  parts  by  weight. 

Silica 30  " 

Tar 5 

(Clark  &  Sabine.) 

Compound  Magnet.— (See  Magnet,  Compound.) 

Compound  Winding  of  Dynamo-Eleetrie  ma- 
chines.— A  method  of  winding  in  which  shunt  and  series 
coils  are  placed  on  the  field  magnets.  (See  Dynamo-Electric 
Machines.) 


WORDS,  TERMS  AND  PHRASES. 


149 


Concentric  Carbon  Electrodes, — (See  Carbons, 
Cored.) 

Condenser,  or  Accumulator. — A  device  for  increasing 
the  capacity  of  an  insulated  conductor  by  bringing  it  near 
another  insulated  earth-connected  conductor,  but  separated 
from,  it  by  a  medium  that  will  readily  permit  induction  to 
take  place  through  its  mass. 

If  the  conductor  A,  Fig.  117,  standing  alone  and  separated 
from  other  conductors,  be  connected  with  an  electric  machine, 
it  will  receive  only  a  very  small  charge. 


Fig.  117. 

If,  however,  it  be  placed  near  C,  but  separated  from  it  by  a 
dielectric,  such  as  a  plate  of  glass  B,  and  C  be  connected  with 
the  ground,  A  will  receive  a  much  greater  charge.  (See  Die- 
lectric.) 

Suppose,  for  example,  that  A  be  connected  with  the  posi- 
tive conductor  of  a  frictional  electric  machine  ;  it  will  by 
induction  produce  a  negative  charge  to  the  surface  of  C, 
nearest  it,  and  repel  a  positive  charge  to  the  earth.  The 
presence  of  these  two  opposite  charges  on  the  opposed  surfaces 
of  A  and  C  produces  a  neutralization  that  permits  A  to 
receive  a  fresh  charge  from  the  machine.  (See  Induction, 
Electrostatic.) 

The  charge  in  a  condenser  in  reality  resides  on  the  opposite 


150  A  DICTIONARY  OF  ELECTRICAL 

surfaces  of  the  glass,  or  other  dielectric  separating  the  metallic 
coatings,  as  can  be  shown  by  removing  the  coatings  after 
charging. 

The  condenser  resulted  from  the  discovery  of  the  Leyden 
jar.    (See  Jar,  Leyden.) 

The  capacity  of  a  condenser  is  meas- 
ured in  microfarads  (See  Farad.) 

a  n  B       In  practice  condensers  are  made  of  sheets 

of  tin  foil,  a,  a,  a,  b,  b,  b,  connected  at 
j.  us.  A.  and  B,  respectively,  and  separated  from 

one  another  by  sheets  of  oiled  silk,  or  thin  plates  of  mica. 
Conducting  Power,  Order  of.— The  ability  of  a  given 
length  and  area  of  cross  section  of  a  substance  to  conduct 
electricity,  as  compared  with  an  equal  length  and  area  of  cross 
section  of  some  other  substance,  such  as  pure  silver  or  copper. 
No  substance  is  known  that  does  not  offer  some  resistance 
to  the  passage  of  an  electric  current. 

The  following  table  is  taken  from  Sylvanus  P.  Thompson's 
"  Elementary  Lessons  in  Electricity  and  Magnetism  :" 

Silver .---1 

Copper  ...  '  -  V  Good  cond uctors. 

Charcoal J 

Water 1 

The  human  body  _- j 

Srywood"  ;  [Partial  conductors. 

Marble | 

Paper J 

Oils 

Poi'celain 

Wood - 

Silk 

Resins... 


Gutta-percha. 

Shellac 

Ebonite 

Paraffin 

Glass 

Dry  air J 


Non-conductors. 


WORDS,  TERMS  AND  PHRASES.  151 

Conductive  Discharge.— (See  Discharge,  Conductive.) 

Conductor,    Anisotropic    —(See    Anisotropic 

Conductor. ) 

Conductor,  Anti-Induction (See  Anti-Induc- 
tion Conductor. 

Conductor,  Conjugate "In  a  system  of 

linear  conductors,  any  pair  of  conductors  are  said  to  be  con- 
jugate to  one  another  when  a  variation  of  the  resistance 
or  the  E.  M.  F.  in  the  one  causes  no  variation  in  the  current 
of  the  other."  (Brought) 

Conductors,  Isotropic (See  Isotropic  Con- 
ductor.) 

Conductors. — Substances  which  will  permit  the  passage 
of  an  electric  current  through  them. 

This  term  is  opposed  to  non-conductors,  or  those  which  will 
not  permit  the  passage  of  an  electric  current  through  them. 

Conduit,  Electric,  Underground A  space  or 

place  for  the  reception  of  electric  wires  or  cables.  (See  Sub- 
way, Electric.) 

Conservation  of  Energy. — The  indestructibility  of  en- 
ergy. 

The  total  quantity  of  energy  in  the  universe  is  unalterable. 

The  total  energy  of  the  universe  is  not,  however,  available 
for  the  production  of  useful  work  for  man. 

When  energy  disappears  in  one  form  it  reappears  in  some 
other  form.  This  is  called  the  correlation  or  conservation  of 
energy.  The  commonest  form  in  which  energy  reappears  is 
as  heat,  and  in  this  case  some  of  the  heat  is  lost  to  the  earth  by 
radiation.  This  degradation,  or  dissipation  of  energy  causes 
some  of  the  energy  of  the  earth  to  become  non-available  to 
man. 

Energy  is  therefore  available  and  non-available.  (See  En- 
tropy.} 


152  A  DICTIONARY  OF  ELECTRICAL 

Consequent  Magnet  Poles.— The  name  given  to  the 
magnetic  poles  formed  by  two  free  N.  poles  or  two  free  S. 
poles  placed  together.  (See  Anomalous  Magnets.) 

Contact  Electricity. — Electricity  produced  by  the  mere 
contact  of  dissimilar  metals. 

The  mere  contact  of  two  dissimilar  metals  results  in  the  pro- 
duction of  opposite  electrical  charges  on  their  opposed  sur- 
faces, or  in  »  difference  of  electric  potential  between  these 
surfaces.  The  mere  contact  of  dissimilar  metals  cannot 
produce  a  constant  electric  current.  An  electric  current 
possesses  kinetic  energy.  To  produce  a  constant  electric  cur- 
rent, therefore,  energy  must  be  expended.  In  the  voltaic  pile 
though  the  contact  of  dissimilar  metals  produces  a  difference 
of  potential,  yet  the  cause  of  the  current  is  to  be  found  in 
chemical  action.  (See  Cell,  Voltaic.) 

Contact-Series.— A  series  of  metals  arranged  in  such  an 
order  that  each  becomes  positively  electrified  by  contact  with 
the  one  that  follows  it. 

The  contact  values  of  some  metals,  according  to  Ayrton 
and  Perry,  are  as  follows  : 

CONTACT-SERIES. 
Difference  of  Potential  in  Volts. 

S£Y::::::::::::::  } «<> 

Lead ]  npo 

Tin { °69 

&:::::::::::;::::} «• 

Iron j 

Copper f  -- 

Copper j 

Platinum f  - - 238 

Platinum ) 

Carbon...  ._  f 113 


WORDS,  TERMS  AND  PHRASES.  153 

The  difference  of  potential  between  zinc  and  carbon  is  equal 
to  1.089,  and  is  obtained  by  adding  the  successive  differences 
between  them. 

This  fact  is  known  technically  as  Yalta's  Law,  which  may  be 
formulated  as  follows : 

The  difference  of  potential  produced  by  the  contact  of  any 
two  metals  is  equal  to  the  sum  of  the  differences  of  potentials 
between  the  intervening  metals  in  the  contact  series. 

Contact  Theory  of  Voltaic  Cell.— (See  Cell,  Vol- 
taic.) 

Contacts.— A  variety  of  faults  occasioned  by  the  accidental 
contact  of  a  circuit  with  any  conducting  body. 

Contacts  of  this  character  are  of  the  following  varieties, 
viz. : 

(1)  Full,  or  Metallic,  as  when  the  circuit  is  accidentally  placed 
in  firm  connection  with  another  metallic  circuit. 

(2)  Partial,  as  by  imperfect  conductors  being  placed  across 
wires,  or  bad  earths,  or  defective  insulation. 

(3)  Intermittent,   as  by  occasional    contacts    of   swinging 
wires,  etc. 

Coiitractures.— In  electro-therapeutics,  a  prolonged  mus- 
cular spasm,  or  tetanus,  caused  by  the  passage  of  an  electric 
current. 

Controlling:  Clocks,  Electric In  a  system  of 

time  telegraphy,  the  master  clock,  whose  impulses  move  or 
regulate  the  secondary  clocks.  (See  Clocks,  Electric.) 

Controlled  Clocks,  Electrically In  a  system 

of  time  telegraphy,  the  secondary  clocks,  that  are  either  driven 
or  controlled  by  the  master  clock.  (See  Clocks,  Electric.) 

Convection,  Electric ;  Convection  Streams. 

—The  air  particles,  or  air  streams,  that  are  thrown  off  from 
the  pointed  ends  of  a  charged,  insulated  conductor. 

Convection  streams,  like  currents  flowing  through  conduct- 
ors, act  magnetically,  and  are  acted  on  themselves  by  mag- 


154  A  DICTIONARY  OF  ELECTRICAL 

nets.  The  same  thing  is  true  of  the  brush  discharge  of  the 
voltaic  arc,  and  of  convective  discharges  in  vacuum  tubes. 

Convection,  Electrolytic A  term  proposed  by 

Helmholtz  to  explain  the  apparent  conduction  of  electricity 
by  an  electrolyte,  without  consequent  decomposition. 

Helmholtz  assumes  that  molecules  of  oxygen  or  hydrogen, 
adhering  to  the  electrodes  during  electrolysis,  are  mechan- 
ically dislodged  and  diffused  through  the  liquid,  thus  car- 
rying off  the  electricity  by  the  charges  received  by  them  while 
in  contact  with  the  electrodes. 

Convection  of  Heat,  Electric A  distribution 

of  heat  during  the  passage  of  a  current  through  an  unequally 
heated  conductor. 

If  the  central  portions  of  a  metallic  bar  are  heated,  the  curve 
of  heat  distribution  is  symmetrical.  On  sending  an  electric 
current  through  the  wire  it  is  heated  according  to  Joule's  law, 
and  the  curve  of  heat  distribution  is  still  symmetrical.  But 
the  current  in  passing  from  the  colder  to  the  hotter  parts  of 
the  wire  produces  an  additional  heating  effect  at  this  point, 
and  in  passing  from  the  warmer  to  the  colder  parts  of  the 
wire,  produces  a  cooling  effect.  (See  Effect,  Peltier.  Effect, 
Thomson.)  The  curve  of  heat  distribution  is  then  no  longer 
symmetrical.  The  term  the  Electrical  Convection  of  Heat 
has  been  given  to  the  dissymmetrical  distribution  of  heat  so 
effected. 

Sir  Wm.  Thomson,  who  studied  these  effects,  found  that 
the  electrical  convection  of  heat  in  copper  takes  place  in  the 
opposite  direction  to  that  in  iron ;  that  is  to  say,  the  electrical 
convection  of  heat  is  negative  in  iron,  (i.  e.,  the  direction  is 
opposite  to  that  of  the  current)  and  positive  in  copper. 

Convective  Discharge.— (See  Discharge,  Convective.) 

Converter,  or  Transformer.— The  inverted  induction 
coil  employed  in  systems  of  distribution  by  means  of  alternat- 
ing currents. 


WORDS,  TERMS  AND  PHRASES. 


155 


A  converter,  or  transformer,  consists  essentially  of  an  induc- 
tion coil  in  which  the  primary  wire,  P  P,  Fig.  119,  is  long  and 
thin,  and  consequently  of  high  electric  resistance  as  compared 
with  the  secondary  wire,  S  S,  which  is  short,  thick,  and  of  low 
resistance. 


Fig.  no. 

To  prevent  heating  and  loss  of  energy  in  conversion,  the 
core  is  thoroughly  laminated.  To  lower  the  magnetic 
resistance,  the  converter  is  iron-clad. 

In  a  system  of  electrical  distribution  by  means  of  trans- 
formers, alternating  currents,  of  small  volume  and  compara- 
tively considerable  difference  of  potential,  are  sent  over  a  line 
from  a  distant  station,  and  passing  into  the  primary  wire  of  a 
number  of  converters,  generally  connected  to  the  line  in  mul- 
tiple-arc produce,  by  induction,  currents  of  comparatively  large 
volume  and  small  difference  of  potential  in  the  secondary 
wires.  Various  electro-receptive  devices  are  conneqtQd,  ia 
multiple-arc  with  the  secondary  wires. 


156 


A  DICTIONARY  OF  ELECTRICAL 


This  method  of  distribution  greatly  reduces  the  cost  of  the 
main  conducting  wires  or  leads  in  certain  cases,  since  consider- 
able energy  may  be  conveniently  sent  over  a  comparatively 
thin  wire,  if  the  difference  of  potential  is  sufficiently  great. 

The  general  arrangement  of  the  converters  on  the  main 


Fig.  120. 

line,  and  the  connection  of  the  secondary  circuits  with  the 
electro-receptive  device  in  such  a  system,  is  shown  in 
Fig.  120.  The  converters  are  supported  on  the  line  poles, 
as  more  clearly  shown  in  Fig.  121,  in  which  the  termi- 
nals of  the  primary  and  secondary  of  the  converter  are  readily 
seen. 

When  the  converter  is  properly  constructed  the  loss  of 
conversion  is  but  small  at  full  load ;  that  is  to  say,  the  watts  in 
the  secondary  are  very  nearly  equal  to  those  in  the  primary. 
A  current  of  10  amperes,  at  2000  volts,  when  passed  into  a 
converter,  the  number  of  whose  turns  in  the  primary  is  t*venty 
times  the  number  in  its  secondary,  will  produce  in  its  sec- 
ondary, a  current  of  200  amperes  at  about  100  volts.  Here, 
the  number  of  watts  in  the  two  cases  is  exactly  the  same, 
or  theoretically  20,000  watts,  In  reality,  it  is  somewhat 


\TORBS,  TERMS  AND  PHRASES. 


15t 


smaller.  In  gen- 
eral, the  shorter 
the  wire  on  the  sec- 
ondary, and  the 
smaller  its  number 
of  turns,  the  great- 
er is  the  reduction 
in  the  difference  of 
potential,  and  the 
greater  is  the  cur- 
rent produced. 

Co-Ordinates, 
Axes  of 

— The  axes  of  ab- 
scissas and  o  r  d  i- 
nates. 

The  two  straight 
lines,  perpendicu- 
lar to  each  other, 
to  which  distances 

rppresonting  v  a  1-  •      Fty-121- 

ues  are  referred  for  the  graphic  representation  of  such  values. 
(See  Abscissas,  Axis  of.) 

Copper  Bath. — (See  Baths,  Copper,  etc.) 

Cords,  Electric Flexible,  insulated  electric  con- 
ductors, generally  containing  at  least  two  parallel  wires. 

They  are  named  from  the  purposes  for  which  thejr  are  em- 
ployed, battery  cords,  dental  cords,  lamp  cords,  motor  cords, 
switch  cords,  etc. 

Core  of  Cable. — The  conducting  wires  of  an  electric 
cable.  (See  Cable,  Electric.) 

Core  Ratio  of  Cable.— The  ratio  between  the  diameter 
of  the  insulator  of  a  cable  and  the  mean  diameter  of  the 
strand. 


158  A  DICTIONARY  OF  ELECTRICAL 

The  core  ratio  is  represented  by  ^  ;  where  D,  is  the  diam- 
eter of  the  insulator,  and  d,  the  mean  diameter  of  the  strand. 
Should  the  extreme  diameter  of  the  strand  of  a  cable  be  used 
in  calculations  for  insulation  resistance,  inductive  capacity, 
etc.,  erroneous  values  would  be  obtained.  The  measured 
diameter  of  the  copper  conductor  is  consequently  decreased 
some  five  per  cent,  by  means  of  which  the  correct  values  are 
approximately  given.  (Clark  &  Sabine.) 

Cored  Carbons.— (See  Carbons,  Cored.) 

Cores,  Armature (See  Armature  Cores.) 

Cores,  Armature,  Ventilation  of Means  for 

the  passage  of  fluids,  such  as  air  through  the  armature  cores 
of  dynamo-electric  machines  so  as  to  prevent  the  undue  ac- 
cumulation of  heat. 

A  properly  proportioned  dynamo-armature  should  need  no 
ventilation,  since  in  such  the  amount  of  heat  generated  is 
small  as  compared  with  the  extent  of  the  radiating  surface. 

Cores,  Lamination  of Structural  subdivisions  of 

the  cores  of  magnets,  armakjres,  and  pole  pieces  of  dynamo- 
electric  machines,  electric  motors,  or  similar  apparatus,  in 
order  to  prevent  heating  and  subsequent  loss  of  energy  from 
the  production  of  local,  eddy  or  Foucault  currents. 

These  laminations  are  obtained  by  forming  the  cores  of 
sheets,  rods,  plates,  or  wires  of  iron  insulated  from  one 
another. 

The  cores  of  armatures  should  be  divided  in  planes  at  right 
angles  to  the  armature  coils  ;  or  in  planes  parallel  to  the  di- 
rection of  the  lines  of  force  and  to  the  motion  of  the  arma- 
ture ;  or  in  general,  in  planes  perpendicular  to  the  currents 
that  would  otherwise  be  generated  in  them. 

Pole  pieces  should  be  divided  in  planes  perpendicular  to 
the  direction  of  the  currents  in  the  armature  wires. 


WORDS,  TERMS  AND  PHRASES.  159 

Magnet  cores  should  be  divided  in  planes  at  right  angles  to 
the  magnetizing  current. 

Cosine. — One  of  the  trigonometrical  functions.  (See 
Trigonometry. ) 

Cotangent. — One  of  the  trigonometrical  functions.  (See 
Trigonometry. ) 

Coulomb.— The  unit  of  electrical  quantity. 

A  definite  quantity  or  amount  of  the  thing  or  effect  called 
electricity. 

Such  a  quantity  of  electricity  as  would  pass  in  one  second 
in  a  circuit  whose  resistance  is  one  ohm,  under  an  electro-mo- 
tive force  of  one  volt. 

The  quantity  of  electricity  contained  in  a  condenser  of  one 
farad  capacity,  when  subjected  to  an  electro-motive  force  of 
one  volt. 

Coulomb- Volt.— A  Joule,  or  .7373  foot  pound. 
The  term  is    generally  written   volt-coulomb.    (See    Volt- 
Coulomb.) 

Counter-EIectro-Motivc  Force.— An  opposed  or  re- 
verse electro-motive  force  produced  in  an  electric  source, 
which  tends  to  produce  a  current  in  the  opposite  direction  to 
that  regularly  produced  by  the  source. 

In  an  electric  motor,  an  electro-motive  force  contrary  to 
that  produced  by  the  current  which  drives  the  motor,  and 
which  is  proportional  to  the  velocity  attained  by  the  motor. 

Counter-electro-motive  force  acts  to  diminish  the  current  in 
the  same  manner  as  a  resistance  would,  and  is  therefore 
sometimes  called  the  spurious  resistance  in  order  to  distin- 
guish it  form  the  ohmic  or  true  resistance. 

Counter-electro-motive  force  is  sometimes  expressed  in 
ohms,  though  it  is  not  true  ohmic  resistance.  (See  Spurious 
Resistance.) 

The  counter-electro-motive  force  of  a  voltaic  battery  is  due 
to  the  polarization  of  the  cells.  Since  this  force  is  due  to  the 


160  A  DICTIONARY  C-F  ELECTRICAL 

current  in  the  cell,  it  can  never  exceed  such  current  or  reverse 
its  direction.  It  may,  however,  equal  il  and  thus  stop  its 
flow.  (See  Polarization  of  Voltaic  Cell.) 

In  a  storage  cell,  the  charging  current  produces  an  electro- 
motive force  counter  to  itself,  which,  as  in  a  motor,  is  a  true 
measure  of  the  energy  stored  in  the  cell.  Economy  requires 
that  the  electro-motive  force  of  the  charging  current  should 
be  as  little  greater  as  possible  than  that  of  the  counter-electro- 
motive force  of  the  cell  it  is  charging. 

In  a  voltaic  arc  a  counter-electvo-motive  force  is  set  up  by 
polarization. 

Counters,'  Electric Various  devices  for  count- 
in0"  and  registering  such  quantities  as  the  number  of  fares 
collected,  gallons  of  water  pumped,  sheets  of  paper  printed, 
revolutions  of  an  engine  per  second,  votes  polled,  etc. 

Various  electric  devices  are  employed 
for  this  purpose.  They  are,  generally, 
electro-magnetic  in  character. 

Couple. — In  mechanics,  two  equal 
parallel  forces  acting  in  opposite  direc- 
tions and  tending  to  cause  rotation. 

The  moment,  or  effective  power  of  a 
couple,  is  equal  to  the  intensity  of  one  of 
Fig.  183.  the  forces  multiplied  by  the  perpendicular 

distance  between  the  directions  of  the  two  forces. 

Couple,   Magnetic The  couple  which  tends  to 

turn  a  magnetic  needle,  placed  in  the  earth's  field,  into  the 
plane  of  the  magnetic  meridian. 

If  a  magnetic  needle  is  in  any  other  position  than  in  the 
magnetic  meridian,  there  will  be  two  parallel  and  equal 
forces  acting  at  A  and  B,  Fig.  122,  in  the  directions  shown  by 
the  arrows.  Their  effect  will  be  to  rotate  the  needle  until  it 
comes  to  rest  in  the  magnetic  meridian  N  S. 

The  total  force  acting  on  either  pole  of  a  needle  free  to 
move  in  any  direction  is  equal  to  the  strength  of  that  pole 


WORDS,  TERMS  AND  PHRASES.  161 

multiplied  by  the  total  intensity  of  the  earth's  .field  at  that 
place,  or,  if  free  to  move  in  a  horizontal  direction  only,  is 
equal  to  the  intensity  of  the  earth's  horizontal  component  of 
magnetism  at  the  place  at  which  the  needle  is  situated,  multi- 
plied by  the  strength  of  that  pole. 

The  effective  power  or  moment  of  the  magnetic  couple  is 
equal  to  the  force  exerted  on  one  of  the  poles  multiplied  by 
the  perpendicular  distance,  P  Q,  between  their  directions. 

Couple,  Thermo-Electrie Any  two  dissimi- 
lar metals  which,  when  connected  at  their  ends  only,  will 
produce  an  electric  current  when  one  set  of  ends  is  heated 
more  than  the  other. 

Couple,  Voltaic •  —The  two  plates  of  dissimilar 

metals,  or  other  substances  in  a  voltaic  battery  which  are 
immersed  in  the  liquid  of  the  cell,  as  for  example,  the  zinc 
and  copper  plates  of  the  simple  voltaic  cell. 

All  voltaic  cells  have  two  metals,  or  a  metal  and  a  metal- 
loid, or  two  gaseous  or  liquid  substances  which  are  of  such  a 
character  that,  when  dipped  into  the  battery  solution,  one 
only  is  chemically  acted  on. 

Each  of  these  substances  is  called  an  element  of  the  cell, 
and  the  two  taken  collectively  form  a  voltaic  couple. 

The  elements  of  a  voltaic  couple  may  consist  of  two  gases 
or  two  liquids.  (See  Gas  Battery.) 

Coupling  of  Voltaic  Cells  or  Other  Electric 
Sources.— A  term  indicating  the  manner  in  which  a  num- 
ber of  separate  electric  sources  are  connected  so  as  to  form  a 
single  source.  (See  Circuits,  Varieties  of.) 

C.  P. — A  contraction  frequently  used  for  candle  power. 
(See  Candle,  Standard.) 

Crater  in  Positive  Cartoon.— The  depression  at  the 
end  of  the  positive  carbon  which  appears  when  a  voltaic  arc  is 
formed.  (See  Arc,  Voltaic.) 


163  A  DICTIONARY  OF  ELECTRICAL 

Creo§oting.— A  process  employed  for  the  preservation  of 
wooden  telegraph  poles  by  injecting  creosote  into  the  pores  of 
the  wood.  (See  Pole,  Telegraphic.) 

Creeping. — The  formation  of  salts  by  efflorescence  on  the 
sides  of  the  porous  cup  of  a  voltaic  cell,  on  the  walls  of  the 
vessel  containing  the  electrolyte,  or  on  the  walls  of  any 
vessel  containing  a  saline  solution. 

Paraffining  the  portions  of  the  walls  out  of  the  liquid,  or 
covering  the  surface  of  the  liquid  with  a  neutral  oil,  obviates 
much  of  this  difficulty.  (See  Efflorescence.) 

Crith. — A  term  proposed  by  A.  W.  Hoffman,  as  a  unit  of 
volume,  or  the  volume  of  one  litre,  or  cubic  decimetre,  of 
hydrogen  at  0°  C.  and  760  mm.  barometric  pressure. 

Critical  Current. — The  current  at  which  a  certain  result 
is  reached. 

Critical  Current  of  a  Dynamo.— That  value  of  the 
current  at  which  the  characteristic  curve  begins  to  depart 
from  a  nearly  straight  line.  (Sylvanus  P.  Thompson.) 

As-  a  rule  the  critical  current  of  a  dynamo 
occurs  when  the  speed  is  such  that  the  electro- 
motive force  is  nearly  two-thirds  the  maximum 
value. 

In  Fig.  123  the  critical  current  is  shown  in 
three  different  cases,  as  occuring  where  the 
dotted  vertical  line  cuts  the  characteristic 
curves. 

The  speed  at  which  a  series  dynamo  excites 
Fig.  123.       itself  is  often  called  the  critical  speed. 

Cro§§,  Electric A  connection,  generally  metallic, 

accidentally  established  between  two  conducting  lines. 

A  defect  in  a  telegraph  or  telephone  circuit  caused  by  two 
wires  coming  into  contact  by  crossing  one  another. 

A  swinging  or  intermittent  cross  is  caused  by  wires  which 
are  too  slack,  being  occasionally  blown  into  contact  by  the 
wind. 


WORDS,  TEEMS  AND  PHRASES.  163 

A  weather  cross  arises  from  defective  action  of  the  insulators 
in  wet  weather. 

Crossing  Wires. — A  device  employed  in  telegraphic 
circuits  whereby  a  faulty  conductor  of  a  telegraph  line  is  cut 
out  of  the  circuit  by  crossing  over  to  a  neighboring,  less  used, 
line. 

To  cut  out  a  faulty  A B C      t       D E 

section  of  wire  in  any  V  / 

circuit,  such  as  C  D,    • • •> '•- «, 

in  the  circuit  ABC*  * 

D  E,  Fig.  124,  a  cross 

connection  is  made  to  a  line  X  Y,  running  near  it,  and  which 

may  be  temporarily  thrown  out  of  use.     By  this  means  the 

interruption  of  an  important  circuit  may  be  avoided. 

Crucible,  Electric A  crucible  in  which  the  heat 

of  the  voltaic  arc,  or  of  electric  incandescence,  is  employed 
either  to  perform  difficult  fusions,  or  for  the  purpose  of 
effecting  the  reduction  of  metals  from  their  ores,  or  the  forma- 
tion of  alloys.  (See  Furnace,  Electric.) 

Crystal.— A  solid  body  bounded  by  symmetrically  disposed 
plane  surfaces. 

A  definite  form  or  shape  is  as  characteristic  of  an  organic 
substance,  as  it  is  of  the  animal  or  plant.  Each  substance  has 
a  form  in  which  it  generally  occurs.  There  are,  however, 
certain  modifications  of  the  typical  form  which  cause  plane 
surfaces  to  appear  curved,  and  the  symmetrical  arrangement 
of  the  faces  to  disappear.  These  modifications  often  render 
it  extremely  difficult  to  recognize  the  true  typical  form. 

For  the  different  fundamental  crystalline  forms,  or  systems 
of  crystals,  see  any  standard  work  on  chemistry. 

Crystallization. — Solidification  from  a  state  of  solution 
or  fusion,  with  the  assumption  of  definite  crystalline  forms. 

The  crystallization  of  a  dissolved  solid  is  favored  by  any 
cause  that  gives  increased  freedom  of  movement  to  the  par- 


164  A  DICTIONARY  OF  ELECTRICAL 

tides  of  the  solid,  such  for  example  as,  solution,  fusion, 
sublimation,  or  precipitation. 

Crystallization  by  Electrical  Decomposition. — 

The  crystalline  deposition  of  various  metals  by  the  passage  of 
an  electric  current  through  solutions  of  their  salts  under 
certain  conditions. 

A  strip  of  zinc  immersed  in  a  solution  of  sugar  of  lead, 
(acetate  of  lead)  soon  becomes  covered  with  bright  metallic 
plates  of  lead,  that  are  electrically  deposited  by  the  weak 
currents  due  to  minute  voltaic  couples  (See  Couple,  Voltaic), 
formed  with  the  zinc  by  particles  of  iron,  carbon,  or  other 
impurities  in  the  zinc.  The  deposit  assumes  at  times  a  tree- 
like growth,  and  is  therefore  called  a  lead  tree. 

Cube,  Faraday's (See  Net,  Faraday's.) 

Current,  Alternating  or  Reversed A  cur- 
rent which  flows  alternately  in  opposite  directions. 
A  current  whose  direction  is  rapidly  reversed. 
The  non-commuted  current  generated  by  the  differences  of 
B                                   potential  in  the  armature  of  a 
dynamo-electric  machine   is  an 
alternating  current. 

In  a  characteristic  curve  of  the 
electro-motive  forces  of  alternat- 
ing currents,  positive  electro- 
motive forces,  or  those  that  would 
produce  currents  in  a  certain 
Fig.  125.  direction,  are  indicated  by  values 

above  a,  horizontal  line,  and  negative  electro-motive  forces, 
by  values  below  the  line. 

The  curves  ABC  and  ODE,  Fig.  125,  are  often  called 
phases,  and  represent  the  alternate  phases  of  the  current. 

Current,  Alternative or  Voltaic  Alterna- 
tives.— A  term  sometimes  used  in  electro-therapeutics  for 
a  sudden  alternating  current.  (See  Alternatives,  Voltaic.) 


WORDS,  TERMS  AND  PHRASES.  165 

Current,  Commuted The  current  of  any  elec- 
tric source  which  produces  alternating  currents,  that  have 
been  caused  to  flow  in  one  and  the  same  direction  by  the  aid 
of  a  commutator.  (See  Commutator.) 

Current,  Continuous An  electric  current  which 

flows  in  one  and  the  same  direction. 

This  term  is  used  in  the  opposite  sense  to  alternating  cur- 
rent. 

Current,  Critical (See  Critical  Current.) 

Current  Density The  quantity  of  current  which 

passes  in  any  part  of  a  circuit  as  compared  with  the  area  of 
cross  section  of  that  part  of  the  circuit. 

In  a  dynamo-electric  machine  the  current  density  in  the  ar- 
mature wire  should  not,  according  to  Sylvanus  P.  Thompson, 
exceed  2,500  amperes  per  square  inch  of  area  of  transverse 
section  of  conductor. 

In  electro-plating,  for  every  definite  current  strength  that 
passes  through  the  bath,  a  definite  weight  of  metal  is  depos- 
ited, the  character  of  which  depends  on  the  current  density. 
The  character  of  an  electrolytic  deposit  will  therefore  depend 
on  the  current  density  at  that  part  of  the  circuit  where  the 
deposit  occurs. 

Current,  Diacritical (See  Diacritical  Cur- 
rent.) 

Current,  Direct A  current  constant  in  direction, 

as  distinguished  from  an  alternating  current. 

Current,  Electric The  quantity  of  electricity 

which  passes  per  second  through  any  conductor  or  circuit,  or 
the  rate  at  which  a  definite  quantity  of  electricity  passes  or 
flows  through  a  conductor  or  circuit. 

An  electric  current  represents  the  ratio  existing  between 
the  electro-motive  force,  causing  the  current,  and  the  re- 
sistance which  may  be  regarded  as  opposing  it.  This  ratio 
is  then  expressed  in  terms  of  quantity  of  electricity  per  second. 


166  A  DICTIONARY  OF  ELECTfctOAL 

The  unit  of  current  or  the  ampere  is  equal  to  one  coulomb 
per  second.  (See  Ampere.  Coulomb.) 

The  word  current  must  not  be  confounded  with  the  mere 
act  of  flowing;  electric  current  signifies  rate  of  flow,  and 
always  supposes  an  electro-motive  force  to  produce  the  cur- 
rent and  a  resistance  to  oppose  it. 

The  electric  current  is  assumed  to  flow  out  from  the  positive 
terminal  or  of  a  source,  through  the  circuit  and  back  into  the 
source  at  the  negative  terminal,  and  is  assumed  to  flow  into 
the  positive  terminal  of  an  electro-receptive  device  such 
as  a  lamp,  motor,  or  storage  battery,  and  out  of  its  nega- 
tive terminal;  or,  in  other  words,  the  positive  pole  of  the  source 
is  always  connected  to  the  positive  terminal  of  the  electro-re- 
ceptive device. 

Current,    Element   of A  term  employed   in 

mathematical  discussions,  to  indicate  a  very  small  part  of  a 
current  in  considering  its  action  on  a  magnetic  needle  or  other 
similar  body. 

Current,  Faradic (See  Faradic  Current.) 

Current  Induction.— (See  Voltaic  Induction.  Electro- 
Dynamics.) 

Current,  Intensity  of. — (See  Intensity  of  Current.) 
Current  Meter. — (See  Galvanometer. ) 

Current,  Reversed A  current  whose  direction 

is  changed  at  intervals.     (See  Current,  Alternating.) 

Current  Reverser. — A  switch,  or  other  apparatus,  to  re- 
verse the  direction  of  a  current. 

Currents,  Amperian (See  Amperian  Currents. 

Magnetism,  Ampere's  Theory  of.) 

Currents,  Diaphragm (See  Diaphragm  Cur- 
rents.) 

Currents,  Earth (See  Earth  Currents.) 


WORDS,  TERMS  AND  PHRASES. 


167 


Currents,  Eddy,  Local,  Foucanlt,  or  Parasit- 
ical   Useless  currents  produced  in  the  metallic 

masses  of  the  pole  pieces,  armatures,  or  field  magnet  cores  of 
dynamo-electric  machines  or  motors,  either  by  the  motion  of 
these  parts  through  magnetic  fields,  or  by  the  variations  in 
the  strength  of  electric  currents  flowing  near  them. 

Eddy  currents  may  even  be  produced  in  the  mass  of  the 
conducting  wire  on  the  armature,  when  this  is  compara- 
tively heavy. 

These  currents  are  called  eddy  currents,  local  currents, 
Foucault  currents,  or  parasitical  currents.  They  form  closed 
circuits  of  comparatively  low  resistance,  and  tend  to  cause 
undue  heating  of  armatures  or  pole  pieces.  They  not  only 
cause  a  useless  expenditure  of  energy,  but  interfere  with  the 
proper  operation  of  the  device. 

To  reduce  them  as  much  as  practicable,  the  pole  pieces  and 
armature  cores  are  laminated.  (See  Cores,  Lamination  of.) 

Since  eddy 
currents  in  dy- 
n  a  m  o  -  electric 
machines  are 
due  to  varia- 
tions in  the  mag- 
netic  strength 
of  the  field  mag-  Fig.  m. 

nets,  or  of  the  armature,  they  will  be  of  greatest  intensity  when 
the  changes  in  the  magnetic  sti  ength  are  the  greatest  and  most 
sudden. 

These  changes  are  most  marked,  and  consequently  the  eddy 
currents  are  particularly  strong,  at  those  corners  of  the  pole 
pieces  of  a  dynamo  from  which  the  armature  is  moved  in  its 
rotation,  as  will  be  seen  from  an  inspection  of  Fig.  126. 

Fig.   127,  shows  eddy  currents  generated  in  pole  pieces. 


A  DICTIONARY  OP  ELECTRICAL 


Fig.  m. 


Currents,  Extra.—  In  a  coil  of  wire  through  which  a  cur- 
rent is  passing,  the  current  produced  by  the  inductive  action 
of  the  current  on  itself  at  the  moment  of  breaking  or  mak- 

ing the  circuit. 
The  extra  cur- 
rent induced  on 
breaking  flows  in 
the  same  direct- 
ion as  the  original 
current  and  acts 
to  strengthen  and 
prolong  it. 

The  extra  cur- 

rent induced  on  making  or  completing  a  circuit,  is  in  the 
opposite  direction,  tending  to  oppose  or  retard  the  current. 

Both  of  these  currents  are  called  induced  or  extra  currents. 
The  former  is  called  the  direct-induced-current,  and  the  latter 
the  reversed-induced-current. 

In  order  to  distinguish  this  induction  from  that  produced  in 
a  neighboring  conductor  by  the  passage  of  the  electric  cur- 
rent, it  is  called  self-induction. 

The  effect  of  the  self-induced  or  extra  currents  on  tele- 
graphic line  is  to  influence  the  speed  of  signaling  by  retard- 
ing the  beginning  of  a  signal,  and  prolonging  its  termina- 
tion. 

The  greater  the  number  of  turns  of  wire  in  a  circuit,  or 
magnet,  and  the  greater  the  mass  of  iron  in  its  core,  the 
greater  the  strength  of  the  extra  current. 


Curreiit§,  Natural- 


— A  term  sometimes  applied  to 


earth  currents.     (See  Earth  Currents.) 

Currents,  Negative  and  Positive A  term  em- 
ployed in  telegraphy  for  currents  sent  over  a  line  in  a  positive 
or  a  negative  direction,  respectively.  (See  Telegraph,  Single- 
Needle.) 


WORDS,  TERMS  AttD  FSRASES.  169 

Currents,  Orders  of Induced  electric  currents 

named  from  the  order  in  which  they  are  induced,  as  currents 
of  the  first,  second,  third,  fourth,  etc.,  orders. 

An  induced  current  can  be  caused  to  induce  another  current 
in  a  neighboring  circuit,  and  this  a  third  current,  and  so  on. 
Such  currents  are  distinguished  by  the  term,  currents  of  the 
second,  third,  fourth,  etc.,  order.  (See  Coils,  Henry's.) 

Currents,  Rectilinear Currents  flowing 

through  straight  or  rectilinear  portions  of  a  circuit. 

In  studying  the  effects  of  attraction  or  repulsion  produced 
by  electric  currents,  the  peculiarity  of  shape  of  any  part  of 
the  circuit  is  often  applied  to  the  current  flowing  through  that 
circuit. 

Currents,  Sinuous A  term  sometimes  applied  to 

currents  flowing  through  a  sinuous  conductor. 

Sinuous  currents  exert  the  same  effects  of  attraction  or 
repulsion  on  magnets,  or  on  other  circuits,  as  would  a  rec- 
tilinear current  whose  length  is  that  of  the  axis  of  such 
current. 

This  can  be  shown  by  approaching  the  circuit  A'B',  Fig. 
128,  consisting  of  the  sinuous  conductor  A',  and  rectilineal- 
conductor  B',  to  the  movable  conductor  ABC  on  which  it 
produces  no  effect.  The  current  A',  therefore,  neutralizes  the 
effects  of  the  current  B';  or,  it  is  equal  to  it  in  effect. 

In  calculating  the  effects  of  sinuous  currents,  it  is  convenient 
to  consider  them  as  consisting  of  a  succession  of  short,  straight 
portions  at  right  angles  to  one  another,  as  shown  in  Fig.  129. 

Currents,  Undulatory Currents  the  strength 

and  direction  of  flow  of  which  gradually  change. 

The  currents  produced  by  all  alternate  current  dynamos  are 
not  of  the  character  generally  known  as  pulsatory,  in  which 
the  strength  and  direction  change  suddenly.  In  actual 
practice,  such  currents  differ  from  undulatory  currents  more 
in  degree  than  in  kind,  since,  when  sent  into  a  line,  the  effects 


170 


A  DICTIONARY  OF  ELECTRICAL 


of  retardation  tend  to  obliterate,  to  a  greater  or  less  extent, 
the  marked  differences  in  intensity  on  which  their  undulatory 
character  depends. 

The  currents  produced  PI 

in  the  coils  of  the  Sie- 
mens' magneto  -  electric 
key,  in  which  the  me- 
chanical to-and-fro  mo- 
tion of  the  key  sends 
electrical  impulses  into 
the  line,  ace,  in  point 
of  fact,  undulatory  in 
character  when  they  fol-  A 
low  one  another  rapidly. 

The  currents  in  most 
d  y  n  a  m  o  -  electric  ma- 
chines, the  number  of 
whose  armature  coils  is 
comparatively  great,  are,  Fig.  128. 

so  far  as  the  variations  in  their  intensity  or  strength  are  con- 
cei*ned,  undulatory  in  character  even  when  non-commuted. 

The  currents  on  all  telephone  lines  that  transmit  articulate 
speech  are  undulatory.  This  is  true,  whether  the  transmitter 
employed  merely  varies  the  resistance  by  variations  of  pres- 
sure, or  actually  employs  makes-and-breaks  that  rapidly  fol- 
low one  another. 

b 


Fig.  129. 

Curve,  Ballistic (See  Ballistic  Curve.) 

Curves,  Characteristic (See    Characteristic 

Curves.) 


WORDS,  TERMS  AND  PHRASES.  171 

Cut-Out,  Automatic for  multiple  Connected 

Electric  Lamp*. — A  device  for  automatically  cutting  a 
lamp  out  of  the  circuit  of  the  leads. 

Automatic  cut-outs  for  incandescent  lamps  when  connected 
to  the  leads  in  multiple-arc,  consist  of  strips  of  readily  melted 
metal  called  safety  fuses,  which  on  the  passage  of  an 
abnormal  current  fuse  and  thus  automatically  break  the  cir- 
cuit in  that  particular  branch.  (See  Safety  Catch.) 

Cut-Out,  Automatic for  Series  Connected 

Lamps. — A  device  whereby  an  electric  arc  lamp  is,  to  all  in- 
tents and  purposes,  automatically  cut  out,or  removed  from  the 
circuit,  by  means  of  a  shunt  of  low  resistance,  which  permits 
the  greater  part  of  the  current  to  flow  past  the  lamp. 

It  will  be  observed  that  the  lamp  is  still  in  the  circuit,  but  is 
to  all  practical  intents  cut  out  from  the  same,  since  the  pro- 
portion of  the  current  that  now  passes  through  it  is  too 
small  to  operate  it. 

In  most  series  arc  lamps  the  automatic  cut-out  is  operated  by 
means  of  an  electro-magnet  placed  in  a  shunt  circuit  of  high 
resistance  around  the  carbons. 

If  the  carbons  fail  to  properly  feed,  the  arc  increases  in 
length  and  consequently  in  resistance.  More  current  passes 
through  the  shunt  magnet,  until  finally,  when  a  cei'tain  pre- 
determined limit  is  reached,  the  armature  of  the  electro-mag- 
net is  attracted  to  the  magnet  pole  and  mechanically  com- 
pletes the  short  circuit  past  the  lamp. 

In  some  automatic  cut-outs  the  fusion  of  a  readily  fused 
wire,  placed  in  a  shunt  circuit  around  the  carbons,  permits  a 
spring  to  complete  the  short  circuit. 

The  automatic  cut-out  prevents  the  accidental  extinguishing 
of  any  single  lamp  in  a  series  circuit  from  extinguishing  the 
entire  circuit. 

Cylindrical  Carbon  Electrodes.  —  (See  Carbons, 
Cored.) 


172  A  DICTIONARY  OF  ELECTRICAL 

Cymogene.— An  extremely  volatile  liquid  which  is  given 
off  from  crude  coal-oil  during  the  early  parts  of  its  distillation. 

The  two  liquids  which  are  obtained  from  the  condensation  of 
the  vapors  given  off  during  the  first  parts  of  the  distillation  of 
crude  coal  oil  are  called  cymogene,  and  rhigolene.  These 
liquids  are  employed  on  account  of  their  extreme  volatility 
for  the  artificial  production  of  cold. 

Rhigolene  is  employed  by  some  for  the  treatment  or  flash- 
ing of  the  carbons  used  in  incandescent  lamps.  (See  Flashing, 
Method  of.} 

Damping. — The  act  of  bringing  a  swinging  magnetic 
needle  quickly  to  rest,  so  as  to  determine  its  amount  of  deflec- 
tion, without  waiting  until  it  comes  to  rest  after  repeated 
swingings  to  and  fro. 

Damping  devices  are  such  as  offer  resistance  to  quick  motion, 
or  high  velocities.  Those  generally  employed  in  electrical  ap- 
paratus are  either  air  or  fluid  friction,  obtained  by  placing  vanes 
on  the  axis  of  rotation,  or  by  checking  the  movements  of  the 
needle  by  means  of  the  currents  it  sets  up,  during  its  motion, 
in  the  mass  of  any  conducting  metal  placed  near  it.  These 
currents,  as  Lenz  has  shown,  always  tend  to  produce  motion 
in  a  direction  opposed  to  that  of  the  motion  causing  them. 
Bell-shaped  magnets  are  especially  suitable  for  this  kind  of 
damping.  (See  Magnet,  Bell-Shaped.) 

The  needle  of  a  galvanometer  is  dead-beat,  when  its  moment 
of  inertia  is  so  small  that  its  oscillations  in  an  intense  field 
are  very  quick,  and  die  out  very  rapidly,  and  the  needle  there- 
fore moves  sharply  over  the  scale  from  point  to  point  and 
comes  quickly  to  a  dead  stop. 

Darnell's  Voltaic  Cell.— (See  Cell,  Voltaic.) 

Dash-Pot.— A  mechanical  device  to  prevent  too  sudden 
motion  in  a  movable  part  of  any  apparatus. 

The  dash-pot  of  an  automatic  regulator,  or  of  an  arc-lamp,  is 
provided  to  avoid  too  sudden  movements  of  the  collecting- 
brushes  on  the  commutator  cylinder,  or  the  too  sudden  fall  of 


WORDS,  TERMS  AND   PHRASES.  173 

the  upper  carbon.  Such  devices  consist  essentially  of  a  loose 
fitting  piston  that  moves  through  air  or  glycerine. 

Dash-pots  are  species  of  damping  devices,  and,  like  the  damp- 
ing arrangements  on  galvanometers  or  magnetic  needles, 
prevent  a  too  free  movement  of  the  parts  with  which  they 
are  connected.  (See  Damping.) 

Dead  -  Beat  Oalvanometer.  —  (See  Galvanometer, 
Dead  Beat.) 

Dead  Earth.— (See  Earths.) 

Dead  Turns  of  Armature  Wire,  or  Dead  Wire. 
— That  part  of  the  wire  on  the  armature  of  a  dynamo -electric 
machine  which  produces  no  useful  electro-motive  force,  or 
i^esultant  current,  on  movement  of  the  armature  through  the 
magnetic  field  of  the  machine. 

The  wire  on  the  inside  of  a  Gramme  or  ring-  armature,  is 
dead-wire. 

Dead- Wires. — Disused  and  abandoned  electric  wires. 

The  term  dead  is  often  applied  to  a  wire  through  which  no 
current  is  passing.  The  term,  however,  is  more  properly 
applied  to  a  wire  formerly  employed,  but  subsequently  aban- 
doned. 

Dead  wires  in  the  neighborhood  of  active  wires  are  a  con- 
stant menace  to  life  and  property,  and  should  invariably  be 
carefully  removed. 

It  is  often  a  matter  of  considerable  importance  to  be  able  to 
determine  whether  or  not  a  current  is  passing  through  a  wire. 
When  the  wire  is  not  inclosed  in  a  moulding,  or  fastened 
against  a  wall,  this  can  readily  be  ascertained  by  bringing  a 
small  compass  needle  near  the  wire,  when  it  will  tend  to  set 
itself  across  the  wire. 

The  term  dead  wire,  as  will  be  seen,  is  used  in  two  distinct 
senses. 

Death,  Electrical  —  —Death  resulting  from  the 
the  passage  of  the  electric  current  through  the  human  body. 


174  A  DICTIONARY   OF  ELECTRICAL 

The  exact  manner  in  which  an  electric  current  causes  death 
is  not  known.  When  the  current  is  sufficiently  powerful,  as 
in  a  lightning  flash,  or  a  powerful  dynamo  current,  insensi- 
bility is  practically  instantaneous. 

Death  may  be  occasioned — 

(1)  As  the  direct  result  of  physiological  shock. 

(2)  From  the  action  of  the  current  on  the  respiratory  centres. 

(3)  From  the  actual  inability  of  the  nerves  or  muscles,  or 
both,  to  perform  their  functions. 

(4)  From  an  actual  electrolytic  decomposition  of  the  blood  or 
other  tissues  of  the  body. 

(5)  From  the  polarization  of  those  parts  of  the  body  through 
which  the  current  passes. 

(6)  From  an  actual  rupture  of  parts  by  a  disruptive  discharge. 
The  current  required  to  cause  death  will  depend  on  a  variety 

of  circumstances,  among  which  are  : 

(1)  The  particular  path  the  current  takes  through  the  body, 
with  reference  to  the  vital  organs  that  may  lie  in  this  path. 

(2)  The  freedom  or  absence  of  sudden  variations  of  electro- 
motive force. 

(3)  The  time  the  current  continues  to  pass  through  the  body. 
In  most  fatal  cases,  it  is  probably  the  extra-current,  or 

the  induced  direct  current  on  breaking,  that  causes  death, 
since,  as  is  well  known,  its  electro-motive  force  may  be 
many  times  greater  than  that  of  the  original  current. 

A  comparatively  low  potential  continuous  current,  cannot, 
therefore,  be  properly  regarded  as  entirely  harmless,  simply 
because  its  electro-motive  force  is  comparatively  small. 

Deci  (as  a  prefix).— The  one-tenth. 

Deci-Lux. — The  one-tenth  of  a  lux.     (See  Lux.) 

Declination,  or  Variation  of  Magnetic  Needle.— 

The  deviation  of  the  magnetic  needle  from  the  true  geograph- 
ical north. 
This  is  often  called  the  variation  of  the  magnetic  needle. 


WORDS,  TEEMS  AND  PHRASES.  175 

The  declination  of  the  magnetic  needle  is  either  E.  or  W. 
(See  Angle  of  Declination.) 

The  declination,  or  variation,  is  different  for  different  parts 
of  the  earth's  surface. 

Lines  connecting  places  which  have  the  same  value  and 
direction  for  the  declination  are  called  isogonal  lines.  A  chart 
on  which  the  isogonal  lines  are  marked  is  called  a  variation 
chart.  (See  Variation  Chart.) 

The  value  of  the  declination  varies  at  different  times. 
These  variations  of  the  declination  are  : 

(1)  Secular,  or  those  occurring  during  rgreat  intervals  of 
time.     Thus  in  1580,  the  magnetic  needle  in  London,  had  a 
variation  of  about  11°  East.     This  eastern  declination   de- 
creased in  1622,  to  6°  E.,  and  in  1680,  the  needle  pointed  to  the 
true  north.     In  1692,  the  declination  was  6°  W.;  in  1730,  13° 
W.;  in  1765,  20°  W.;  and  in  1818,  the  needle  reached  its  great- 
est western  declination  and  is  now   moving  eastwards.      The 
declination,  however,  is  still  west. 

(2)  Annual,  the  needle  varying  slightly  in  its  declination 
during  different  seasons  of  the  year. 

(3)  Diurnal,  the  needle  varying  slightly  in  its  declination 
during  different  hours  of  the  day. 

(4)  Irregular,  or  those  which  occur  during  the  prevalence 
of  a  magnetic  storm. 

It  has  been  discovered  that  the  occurrence  of  a  magnetic 
storm  is  simultaneous  with  the  occurrence  of  an  unusual  num- 
ber of  sun  spots.  (See  Sun  Spots.) 

Declinometer. — A  magnetic  needle  suitably  arranged  for 
the  measurement  of  the  value  of  the  magnetic  declination  or 
variation,  of  any  place. 

Decomposition. — In  chemistry,  the  separation  of  a  mole- 
cule into  its  constituent  atoms  or  groups  of  atoms.  (See  Mole- 
cule. Atom.) 

Decomposition,  Electric  or  Electrolytic  

— The  separation  of  a  molecule  into  its  constituent  atoms 


176  A  DICTIONARY  OF  ELECTRICAL 

or  groups  of  atoms  by  the  action  of  the  electric  current. 
These  atoms  or  groups  of  atoms  are  either  electro-positive 
or  electro-negative  in  character.  (See  Electrolysis.  Anion. 
Kathion.) 

Deflagration  of  Metal§,  Electrical 

The  heating  of  metallic  substances  by  the  electric  current 
to  a  temperature  at  which  they  rapidly  fuse  and  volatilize. 

Deflagrator,  Hare's The  name  given  to  a 

voltaic  battery,  of  small  internal  resistance,  employed  by  Hare 
in  the  deflagration  of  metals  by  the  electric  current. 

Deflection'  of  Magnetic  Needle.— The  movement  of 
a  needle  out  of  a  position  of  rest  in  the  earth's  magnetic  field, 
or  in  the  field  of  another  magnet,  by  the  action  of  an  electric 
current,  or  another  magnet. 

Deflection  Method.— A  method  employed  in  electrical 
measurements,  as  distinguished  from  the  zero  method,  in 
which  a  deflection  produced  on  any  instrument  by  a  given 
current,  or  by  a  given  charge,  is  utilized  for  determining  the 
value  of  that  current  or  charge. 

The  conditions  remaining  the  same,  the  same  current  or 
charge  will  produce  the  same  deflection  at  any  time.  Differ- 
ent deflections  produced  by  currents  or  charges,  the  values  of 
which  are  unknown,  are  determined  by  certain  ratios  existing 
between  the  deflections  and  the  currents  or  charges.  These 
ratios  are  determined  experimentally  by  the  calibration  of  the 
instrument.  (See  Calibration.) 

Deflection  methods  are  opposed  to  zero  or  null  methods,  in 
which  latter  a  balance  of  opposite  electro-motive  forces,  or  a 
proportionally  equal  fall  of  electric  potential,  is  ascertained  by 
the  failure  of  a  needle  to  be  moved  by  a  current  or  a  charge. 

Degradation  of  Energy. — Such  a  dissipation  of  energy 
as  to  render  it  non-available  to  man.  (See  Conservation  of 
Energy.  Entropy.) 

Deka  (as  a  prefix).— Ten  times. 


WORDS,  TERMS  AND  PHRASES.  177 

Demagnetization.— A  process  generally  directly  oppo- 
site to  that  for  producing  a  magnet,  by  means  of  which  the 
magnet  may  be  deprived  of  its  magnetism. 

A  magnet  may  be  deprived  of  its  magnetism,  or  be  demag- 
netized— 

(1)  By  heating  it  to  redness. 

(2)  By  touching  to  its  poles  magnet  poles  of  the  same  name 
as  its  own. 

(3)  By  reversing  the  directions  of  the  motions  by  which  its 
magetism  was  originally  imparted,  if  magnetized  by  touch. 

(4)  By  exposing  it  in  a  helix  to  the    influence  of  currents 
which  will  impart  magnetism  opposite  to  that  which  it  origi- 
nally possessed. 

Demagnetization  of  Watches.— (See  Watches,  De- 
magnetization of.) 

Density  of  Charge. — (See  Charge,  Density  of.) 
Density  of  Current. — (See  Current,  Density  of.) 
Density,  Magnetic  —       -  — (See  Magnetic  Density.) 

Dental  Dfallet,  Electro-Magnetic A  mal- 
let for  filling  teeth,  the  blows  of  which  are  struck  by  means 
of  electrically  driven  mechanism. 

Electro-magnetism  was  first  employed  for  this  purpose  by 
Bonwill  of  Philadelphia. 

Depolarization. — The  act  of  breaking  up  or  I'emoving 
the  polarization  of  a  voltaic  cell  or  battery.  (See  Polarization 
of  Voltaic  Cell.) 

Deposit,  Electro-metallurgical The  deposit 

of  metal  obtained  by  electro-metallurgical  processes. 

To  obtain  a  good  metallic  deposit  the  density  of  the  current 
must  be  regulated  according  to  the  strength  of  the  metallic 
solution  employed. 

Electro-metallurgical  deposits  are  either— 


178  A  DICTIONARY  OF  ELECTRICAL 

(1)  Reguline,  or   flexible,  adherent,  and  strongly  coherent 
metallic  films,  deposited  when  neither  the  current  nor  the 
solution  is  too  strong. 

(2)  Crystalline,  or  non-adherent  and  non-coherent  deposits. 

The  crystalline  deposit  may  either  be  of  a  loose,  sandy  char- 
acter, which  is  thi*owndown  when  too  feeble  a  current  is  used 
with  too  strong  a  metallic  solution,  or  it  may  consist  of  a  black 
deposit,  which  is  thrown  down  when  the  current  is  too  strong  as 
compared  with  the  strength  of  the  solution.  This  latter  char- 

G  acter    of    deposit    is  sometimes    technically 

called  burning,  and  takes  place  most  fre- 
quently at  sharp  corners  and  edges,  where  the 
current  density  is  greatest.  (See  Density  of 
Current.) 

Derived  Circuit.— A  term  applied  to  a 
shunt  circuit. 

If  the  conductor  S,  Fig.  130,  be  connected 
with  the  circuit  of  the  battery  B,  a  derived 
F-,g.  130.          circuit  will  thus  be  established,  and  a  current 
will  flow  through  S,  thus  diminishing  the  current  in  the  gal- 
vanometer.    (See  Shunt  Circuit.) 
Derived  Units.— (See  Units,  Derived.) 
Destructive  Distillation.— (See  Distillation,  Destruc- 
tive.) 

Device,  Safety for  multiple  Circuits.— (See 

Safety  Catch.) 

Device,    Safety for     Series     Circuits.— (See 

Device,  Safety,  for  Arc  Lamps.) 

Device,  Electro-Receptive Various  devices 

placed  in  an  electric  circuit,  and  energized  by  the  passage 
through  them  of  the  electric  current. 

The  following  are  among  the  more  important  electro-recep- 
tive devices,  viz. : 

(1)  Electro-Magnet 

(2)  Electric  Motor, 


WORDS,  TERMS  AND  PHRASES.  179 

(3)  An  Arc  or  Incandescent  Lamp. 

(4)  An  Uncharged  Storage  Cell. 

(5)  An  Electric  Heater. 

(6)  A  Plating  Bath,  or  Voltameter. 

(7)  A  Telegraphic  or  Telephonic  Instrument. 

(8)  Electro-Magnetic  Signal  Apparatus. 

I >r\l ror*ii I  Helix.— (See  Helix,  Dextrorsal) 

Diacritical  Current.— Such  a  strength  of  the  magnetiz- 
ing current  as  produces  a  magnetization  of  an  iron  core  equal 
to  half  saturation. 


Fig.  131. 

Diacritical  Number. — Such  a  number  of  ampere-turns 
at  which  a  given  core  would  receive  a  magnetization  equal  to 
half  saturation. 

Diacritical  Point  of  Magnetic  Saturation.— A  term 

proposed  by  S.  P.  Thompson  for  such  a  value  of  the  coefficient 
of  magnetic  saturation,  that  the  core  is  magnetized  to  exactly 
one-half  its  possible  maximum  of  magnetization. 


180  A  DICTIONARY  OF  ELECTRICAL 

Diagnosis,  Electro The  determination  of  the 

healthy  or  diseased  condition  of  different  parts  of  the  human 
body  by  the  character  and  extent  of  the  muscular  contrac- 
tions on  electrical  excitation  of  the  nerves  or  muscles. 

Diagometer,  Rousseau's An  apparatus 

in  which  an  attempt  is  made  to  determine  the  chemical  com- 
position and  consequent  purity  of  certain  substances  by  their 
electrical  conducting  powers. 

The  arrangement  of  the  apparatus  is  shown  in  Fig.  131.  A 
dry  pile  A,  has  its  negative,  or  — ,  terminal  m',  grounded.  Its 
positive,  or  -}->  terminal  is  connected  to  a  delicately  supported, 
and  slightly  magnetized  needle  M,  terminated  by  a  conducting 
plate  L.  Opposite  L,  and  at  the  same  height,  is  a  fixed  plate 
of  slightly  larger  size.  The  needle  M,  when  at  rest  in  the 
plane  of  the  magnetic  meridian,  is  in  contact  at  L  with  the 
fixed  plate.  If,  therefore,  the  upper  plate  of  the  pile  is  con- 
nected with  the  needle  M  both  plates  are  similarly  charged 
and  repulsion  takes  place,  the  needle  coming  to  rest  at  a 
certain  distance  from  the  fixed  plate. 

The  substance  whose  purity  is  to  be  determined  is  placed  in 
the  cup  G,  which  is  connected  through  L  with  the  fixed  plate. 
A  branch  wire  from  the  -|-  terminal  of  the  pile  is  then  clipped 
into  the  substance  in  G,  and-ts  purity  determined  from  the 
length  of  time  required  for  the  two  plates  at  L  to  be  dis- 
charged through  the  material  in  G, 

It  is  claimed  that  the  instrument  will  detect  the  difference 
between  pure  coffee  and  chicory.  Its  practical  application, 
however,  is  very  doubtful. 

Diagram,  Thermo-Electric A  diagram  in 

which  the  thermo-electric  power  between  different  metals  is 
designated  for  different  temperatures. 

The  differences  of  potential,  produced  by  the  mere  contact  of 
two  metals,  varies,  not  only  with  the  kind  of  metals,  and  the 
physical  state  of  each  metal,  but  also  with  their  temperature. 
This  difference  of  potential,  maintained  in  consequence  of 


WORDS,  TERMS  AND  PHRASES. 


181 


the  difference  of  temperature  between  the  junctions  of  a 
thermo-electric  couple,  is  approximately  proportional  to  the 
differences  of  temperature  of  these  junctions,  if  these  dif- 
ferences are  not  great,  and  is  equal  to  the  product  of  such 
differences  of  temperature  and  a  number  dependent  on  the 
metals  in  the  couple.  This  number  is  called  the  thermo- 
electric power.  (See 
Couple,  Thermo-Elec- 
tric.  Thermo-Electric 
Power.) 

In  Fig.  182  (after 
Tait),  the  thermo- 
electric power  is 
shown  between  lead  Fi&- 1S2- 

and  iron,  and  lead  and  copper.  The  numbers  at  the  top  of  the 
table  represent  degrees  of  the  Centigrade  thermometer. 
Those  at  the  sides  represent  the  differences  of  potential  in 
micro-volts. 

The  thermo-electric  power  of  the  lead-iron  couple  decreases 
from  the  freezing  point  of  water,  0°  C.,  to  a  temperature  of 
274°. 5  C.,  when  it  becomes  zero.  Beyond  that  temperature 
the  thermo-electric  power  increases,  but  in  the  opposite 
direction.  The  point  at  which  this  occurs  is  called  the  neu- 
tral point. 

Dial  Telegraph.— (See  Telegraphy,  Step-by-Step.) 

Diamagiietie.— A  term  applied  to  the  property  possessed 
by  substances  like  bismuth,  phosphorus,  antimony,  zinc  and 
numerous  others,  which  are  apparently  repelled  when  placed 
between  the  poles  of  powerful  magnets. 

When  diamagnetic  substances  in  the  form  of  rods  or  bars 
are  placed,  as  in  Fig.  134,  between  the  poles  A  and  B  of  a 
powerful  electro-magnet,  they  place  themselves  at  right 
angles  to  the  poles,  or  are  apparently  repelled. 


182 


A  DICTIONARY  OP  ELECTRICAL 


Paramagnetic  substances  like  iron  or  steel,  on  the  contrary, 
come  to  rest  under  similar  circumstances  in  a  straight  line 
joining  the  poles,  as  in  the  position  shown  in  the  annexed 
figure. 

Paramagnetic  substances  are  some- 
times called  ferro  -  magnetic,  or  sub- 
stances magnetic  after  the  manner  of 
iron.  This  word  is  unnecessary  and  ill. 
advised.  The  term  sidero-magnetic  has 
also  been  proposed  in  place  of  paramag- 
netic. 

Paramagnetic  substances  appear  to 
concentrate  the  lines  of  magnetic  force 
on  them;  that  is,  their  magnetic  resist- 
ance is  smaller  than  that  of  the  air  or 
other  medium  in  which  the  magnet  is 
Fig.  1SU.  placed.  They  therefore  come  to  rest 

with  their  greatest  dimensions  in  the  direction  of  the  lines  of 
magnetic  force. 

Diamagnetic  substances  appear  to  have  a  greater  magnetic 
resistance  than  that  of  the  air  around  them.  They  therefore 
come  to  rest  with  their  least  dimensions  in  the  direction  of 
the  lines  of  magnetic  force. 

The  difference  between  paramagnetic  and  diamagnetic  sub- 
stances is  believed  by  some  to  be  due  to  the  resistance  they 
thus  offer  to  lines  of  magnetic  force  as  compared  with  that 
offered  by  air  or  by  a  vacuum. 

The  action  of  magnetism,  however,  on  gaseous  media,  ro- 
tating a  plane  of  polarized  light  to  the  right,  in  some  gases, 
and  to  the  left  in  others,  shows  that  the  real  nature  of  these 
phenomena  is  yet  unknown. 

Tyndall  comes  to  the  conclusion  as  the  result  of  extended 
experimentation,  "that  the  diamagnetic  force  is  a  polar  force, 
the  polarity  of  diamagnetic  bodies  being  opposed  to  that  of 


WORDS,  TERMS  AND  PHRASES.  183 

paramagnetic  ones  under  the  same  conditions  of  excitement." 
(See  Tyndall,  on  Diamagnetism.) 

Diamagnetism  is  also  possessed  by  certain  liquid  and  gas- 
eous substances. 

Diamagnetic  Polarity.— (See  Polarity,  Diamagnetic.) 

Diamagnetism. — A  term  applied  to  the  magnetism  of  dia- 
magnetic  bodies.  (See  Diamagnetic.) 

Diameter  of  Commutation.— In  a  dynamo-electric 
machine,  a  diameter  on  the  commutator  cylinder  on  one 
side  of  which  the  differences  of  potential,  produced  by  the 
movement  of  the  coil  through  the  magnetic  field,  tend  to  pro- 
duce a  current  in  a  direction 
opposite  to  those  on  the 
other  side. 

Thus,  in  Fig.  133,  the  di- 
rections of  the  induced  elec- 
tro-motive, forces  are  indi- 
cated by  the  arrows.  The 
diameter  of  commutation  is 
therefore  the  line  n  n'.  The 
term  neutral  line  is  also  \nf 

sometimes  given  to  this  line.  fiff- 133. 

It  lies  at  right  angles  to  the  line  of  maximum  magnetization. 

In  an  armature  with  closed-circuited  coils,  that  is,  in  an 
armature  in  which  the  armature  coils  are  connected  in  a 
closed  circuit,  the  collecting  brushes  rest  on  the  commutator 
cylinder  at  the  neutral  line,  or  on  the  diameter  of  commuta- 
tion. 

In  an  open  circuited  armature,  however,  where  the  coils 
are  independent  of  each  other,  the  collecting  brushes  must  be 
set  at  m  m,  at  right  angles  to  the  neutral  line  n  n.  The  term 
diameter  of  commutation  is,  therefore,  often  applied  to  this 
second  position.  According  to  this  use  of  the  term,  the  diame- 
ter of  commutation  is  that  diameter  on  the  commutator 
which  joins  the  points  of  contact  of  the  collecting  brushes. 


184  A  DICTIONARY  OF  ELECTRICAL 

The  neutral  line  n  n,  Fig.  133,  it  will  be  noticed  does  not 
occupy  a  vertical  position,  but  is  displaced  somewhat  in  the 
direction  of  rotation,  thus  necessitating  the  shifting  of  the 
brushes  forward  in  the  direction  of  rotation.  This  necessary 
shifting  of  the  brushes  is  known  technically  as  the  Lead  of  the 
Brushes.  (See  Angle  of  Lead.) 

It  will  thus  be  seen  that  the  term  diameter  of  commutation 
is  used  in  different  senses. 

In  reality,  the  term  refers  lo  the  position  of  certain  points 
on  the  commutator  as  distinguished  from  points  on  the  arma- 
ture coils.  On  the  commutator,  the  diameter  of  commutation 
is  the  line  drawn  through  the  two  commutator  bars  at  which 
the  currents  from  the  two  sides  are  opposed  to  each  other. 

It  is  evident  that  the  commutator  may  be  intentionally 
twisted  with  respect  to  the  armature,  so  as  to  bring  its  diam- 
eter of  commutation  into  any  desired  convenient  position. 

Diaphragm. — A  sheet  of  some  solid  substance,  generally 
elastic  in  character  and  circular  in  shape,  securely  fixed  at  its 
edges  and  capable  of  being  set  into  vibration. 

The  receiving  diaphragm  of  a  telephone  is  generally  a  rigid 
plate  or  disc  of  iron  fixed  at  its  edges,  placed  near  a  magnet 
pole,  and  set  into  vibration  by  variations  in  the  magnetic 
strength  of  the  pole  due  to  variations  in  the  current  that  is 
passed  over  the  line. 

The  diaphragm  of  the  transmitting  telephone,  or  of  a  pho- 
nograph, consists  of  a  plate,  fixed  at  its  edges  and  set  into 
vibration  by  the  sound  waves  striking  it. 

Diaphragm  Currents.— Electric  currents  produced  by 
forcing  a  liquid  through  the  capillary  pores  of  a  diaphragm. 
(See  Osmose,  Electric.) 

Diaphragm  of  Voltaic  Cell. — A  term  sometimes 
used  for  the  porous  cell  of  a  double  fluid  voltaic  cell.  (See 
Porous  Cell.  Cell,  Voltaic.) 

Dielectric.— A  substance  which  permits  induction  to  take 
place  through  its  mass. 


WORDS,  TERMS  AXD  PHRASES.  185 

The  substance  which  separates  the  opposite  coatings  of  a  con- 
denser is  called  the  dielectric.  All  dielectrics  are  non-con- 
ductors. 

All  non-conductors  or  insulators  are  dielectrics,  but  their 
dielectric  power  is  not  exactly  proportional  to  their  non-con- 
ducting- power. 

Substances  differ  greatly  in  the  degree  or  extent  to  which 
they  permit  induction  to  take  place  through  or  across  them. 
Thus,  a  certain  amount  of  inductive  action  takes  place 
between  the  insulated  metal  plates  of  a  condenser  across  the 
layer  of  air  between  them. 

Dielectric  Capacity,  or  Dielectric  Constant.— A 

term   employed    in    the    same    sense    as    specific    inductive 
capacity.     (See  Capacity,  Specific  Inductive.) 

Dielectric  Strain.— The  strained  condition  in  which  the 
glass,  or  other  solid  dielectric  of  a  condenser,  is  placed  by  the 
charging  of  the  condenser. 

The  stress  in  this  case,  i.  e.,  the  force  producing  the  defor- 
mation or  strain,  is  the  attraction  of  the  opposite  charges. 
This  stress,  in  the  case  of  a  Leyden  jar,  is  often  sufficiently 
great  to  cause  a  rupture  of  the  glass. 

Difference  of  Potential.— A  term  employed  to  denote 
that  portion  of  the  electro-motive  force  which  exists  between 
any  two  points  in  a  circuit. 

The  difference  of  potential  at  the  poles  of  any  electric  source, 
such  as  a  battery  or  dynamo,  is  that  portion  of  the  total  elec- 
tro-motive force  which  is  available,  and  is  equal  to  the  total 
electro-motive  force,  less  what  is  lost  in  the  source.  (See 
Potential.  Electro-Motive  Force.) 

Differential  Galvanometer.— A  galvanometer  in 
which  the  needle  is  deflected  by  the  action  of  two  parallel 
coils,  the  currents  in  which  are  opposed  to  each  other.  (See 
Galvanometer,  Differential.) 


A  DICTIONARY  OF  ELECTRICAL 


Differential  Inductometer.— (See  Inductometer,  Dif- 
ferential) 

Differential  Thermo-Pile.— A  thermo-pile  ia  which 
both  faces  of  the  pile  are  exposed  to  the  action  of  two  nearly 
equal  sources  of  heat  in  order  to  determine  accurately  the 
difference  in  their  intensities.  (See  Thermo-Pilc.) 

Differential  Voltameter. — (See  Voltameter,  Differen- 
tial.} 

Diffusion  of  Electric  Current.— A  term  employed 
mainly  in  electro-therapeutics  to  designate  the  difference  in 
the  density  of*  current  in  different  portions  of  the  human 
body,  or  other  conductor. 

When  the  electrodes  are  placed  at  any  two  given  points  of 
the  human  body,  the  current  branches  through  various  paths, 
extending  in  a  general  direction 
from  one  electrode  to  the  other, 
according  to  the  law  of  branch 
or  derived  circuits,  and  flowing 
in  greater  amount,  or  with 
greater  density  of  current, 
through  the  relatively  better 
conducting  paths.  (See  Den- 
sity of  Current.) 

Dimensions  of  Acceler- 
a  t  i  o  11 . —  (See  Acceleration, 
Unit  of.) 

Dip,  Magnetic 

The  deviation  of  the  magnetic 
needle  from  a  horizontal  posi- 
tion. 

>  The  inclination  of  the  mag- 
netic needle  towards  the  earth. 
The  magnetic  needle  shown 
in  Fig.  135,  though  supported  at  its  centre  of  gravity  will  not 
retain  a  horizontal  position  in  all  places  on  the  earth's  surface. 


WORDS,  TERMS  AND  PHRASES. 


187 


In  the  Northern  Hemisphere  its  north-seeking  end  will  dip 
or  incline  at  an  angle  B  O  C,  called  the  angle  of  dip.  In 
the  Southern  Hemisphere  its  south-seeking  end  will  dip. 

The  cause  of  the  dip  is  the  unequal  distance  of  the  mag- 
netic poles  of  the  earth  from  the  poles  of  the  needle. 

The  Magnetic  Equator  is  a  circle  passing  around  the  earth 
midway  (in  intensity)  between  the  earth's  magnetic  poles. 
There  is  no  dip  at  the  magnetic  equator.  At  either  magnetic 
pole  the  angle  of  dip  is  90°. 

Dipping  Circle,  or  Inclination  Compas§.— A  mag- 
netic needle  moving  freely  in  a 
single  vertical  plane,  and  em- 
ployed for  determining  the  an- 
gle of  dip  at  any  place. 

The  needle  M,  Fig.  136,  is  sup- 
ported on  knife  edges  so  as  to 
be  free  to  move  only  in  the 
vertical  plane  of  the  graduated 
vertical  circle  C  C.  This  circle 
is  movable  over  the  horizon- 
tal graduated  circle  H  H.  In 
order  to  determine  the  true 
angle  of  dip,  the  vertical  plane 
in  which  the  needle  is  free  to 
move  must  be  placed  exactly 
in  the  plane  of  the  magnetic 
meridian. 

To  ascertain  this  plane  the 
vertical  circle  is  moved  until  the  needle  points  vertically 
downwards.  It  is  then  in  a  plane  90°  from  the  magnetic 
meridian.  The  vertical  circle  is  then  moved  over  the  hori- 
zontal circle  90°,  in  which  position  it  is  in  the  plane  of  the 
magnetic  meridian,  when  the  true  angle  of  dip  is  read  off. 

For  an  explanation  of  the  reason  of  this  see  Component, 
Horizontal  and  Vertical,  of  the  Earth's  Magnetism. 


18$  A  DICTIONARY  OP  ELECTRICAL 

Dipping,    Electro-Metallurgical    Deposition   by 

— The  process  of  obtaining  a  metallic  deposit  on  a 


metallic  surface  by  dipping  it  in  a  solution  of  a  readily  decom- 
posable metallic  salt. 

A  bright,  polished  iron  surface,  when  simply  dipped  into  a 
solution  of  copper  sulphate,  receives  a  coating  of  metallic  cop- 
per from  the  electrolytic  action  thus  set  up. 

This  process  is  known  technically  as  dipping.  The  term 
dipping  is  also  used  in  electro-metallurgy  to  indicate  the  pro- 
cess of  cleaning  the  articles  that  are  to  be  electro-plated  by 
dipping  them  in  various  acid  or  alkaline  baths. 

Direct  Current.— (See  Current,  Direct.) 

Direct  Induced  Current.— The  current  induced  in  a 
circuit  by  induction  on  itself,  or  self  induction,  on  breaking 
the  circuit.  (See  Extra  Current.) 

Direction  of  Lines  of  Force.— The  direction  in  which 
it  is  assumed  the  lines  of 
magnetic  force  pass. 

It  is  generally  agreed  to 
consider  the  lines  of  mag- 
netic force  as  coming  out 
of  the  north  pole  of  a  mag- 
net and  passing  into  its 
south  pole,  as  shown  in 
Fig.  137. 

This  is  sometimes  called  the  positive  direction  of  the  lines 
of  force,  and  agrees  in  general  with  the  direction  in  which 
the  electric  current  is  assumed  to  flow,  which  is  from  the 
positive  to  the  negative.  That  is  to  say,  the  lines  of  mag- 
netic force  are  assumed  to  flow  or  pass  out  of  the  north  pole 
and  into  the  south  pole  of  a  magnet.  Of  course  there  is  no 
evidence  of  any  flow,  or  any  particular  direction  as  character- 
izing them.  (See  Field,  Magnetic.) 


WORDS,  TERMS  AND  PHRASES.  189 

Directive  Power  of  Magnetic  Needle.— The  ten- 
dency of  a  magnetic  needle  to  move  so  as  to  come  to  rest  in 
the  direction  of  the  lines  of  the  earth's  magnetic  field. 

The  directive  power  of  the  needle  is  due  to  the  attraction  of 
the  earth's  magnetic  poles  for  the  poles  of  the  needle,  or  to 
the  action  of  the  earth's  magnetic  field.  Since  the  force  of 
the  earth's  magnetism  forms  a  couple,  there  is  no  tendency 
for  the  needle  to  move  towards  either  of  the  earth's  poles, 
but  merely  to  rotate  until  it  comes  to  rest  with  the  lines  of 
the  earth's  magnetic  field  passing  through  its  poles.  (See 
Couple,  Magnetic.) 

Of  course  this  would  be  true  in  the  case  of  a  directing  mag- 
iu-t  only  when  it  is  at  a  great  distance  from  the  needle. 
Otherwise  there  would  be  attraction  as  well  as  rotation. 


Fig.  138. 

,  Arago's A  copper  or  other  non-magnetic 

metallic  disc,  which,  when  rapidly  rotated  under  a  magnetic 
needle,  supported  independently  of  the  disc,  causes  the 
needle  to  be  deflected  in  the  direction  of  rotation,  and,  when 
the  velocity  of  the  disc  is  sufficiently  great,  to  rotate  with  it. 

Such  a  disc  is  shown  in  Fig.  138,  at  B.  The  movement  of 
the  needle  is  due  to  electric  currents,  induced  by  the  disc 
moving  through  the  field  of  the  needle  so  as  to  cut  its  lines  of 


190  A  DICTIONARY  OF  ELECTRICAL, 

magnetic  force.  To  obtain,the  best  results  the  disc  must  move 
very  rapidly,  and  should  be  near  the  needle.  Moreover,  the 
needle  should  be  very  powerful. 

This  effect  was  discovered  by  Arago,  in  1824.  Since  a  mag- 
netic needle  moving  over  a  metallic  plate  produces  electric 
currents  in  a  direction  which  tend  to  stop  the  motion  of  the 
needle,  a  damping  of  the  motion  of  a  magnetic  needle  is  some- 
times effected  by  causing  it  to  move  near  a  metal  plate. 
The  induced  currents  which  the  needle  produces  in  the  plate 
by  its  motion  over  it  tend  to  retard  the  motions  of  the  needle. 
(See  Damping.  Lenz's  Law.} 

Disc  Armature.— (See  Dynamo-Electric  Machine,  Arma- 
tures.) 

Disc,  Faraday's A  metallic  disc  movable  in  a 

magnetic  field  on  an  axis  par- 
allel to  the  direction  of  the 
field. 

Such  a  disc  is  shown  in  Fig. 
139,   and  moves,   as   will  be 
seen,  so  as  to  cut  the  lines 
of   magnetic  force    at    right 
Fig.  139.  angles. 

The  difference  of  potential  generated  by  the  motion  of  such 
a  disc  may  be  caused  to  produce  a  current,  by  providing  a  cir- 
cuit which  is  completed  through  the  portion  of  the  disc  that  at 
any  moment  of  its  rotation  is  situated  between  spring  con- 
tacts resting  on  the  axis  of  rotation  and  the  circumference  of 
the  disc,  respectively. 

In  Barlow's,  or  Sturgeon's  Wheel,  Fig.  140,  the  wheel  itself 
rotates  in  the  direction  shown,  when  a  current  is  sent  through 
it  in  a  direction  indicated  by  the  arrows. 

Discharge.— The  equalization  of  the  difference  of  poten- 
tial between  the  terminals  of  a  condenser  or  source,  on  their 
connection  by  a  conductor, 


WORDS,  TERMS   AND  PHRASES.  191 

The  removal  of  a  charge  from  the  surface  of  any  charged 
conductor  by  connecting  it  with  the  earth,  or  another  conduc- 
tor, effects  its  discharge. 

The  discharge  of  an  insulated  conductor,  a  cloud,  a  con- 
denser, or  a  Leyden  battery,  is  but  momentary,  and  a  cur- 
rent results  which  rap- 
idly passes  from  its  max- 
imum value  to  zero. 

The  discharge  of  a  vol- 
taic battery,  or  a  storage 
battery,  is  nearly  contin- 
uous, and  furnishes  a 
current  which  is  practi-  •!%•  ll»°- 

cally  continuous,  as  distinguished  from  the  momentary  current 
produced  by  the  discharge  of  a  condenser. 

A  discharge  may  be  Conductive,  Convective,  or  Disruptive. 

Discharge,  Conductive •  —A  discharge  effected 

by  leading  the  charge  off  through  a  conductor  placed  in  con- 
tact with  the  charged  body. 

Discharge,  Convective The  discharge  which 

occurs  from  the  points  of  a  highly  charged  conductor,  through 
the  repulsion  by  the  conductor  of  air  particles  that  carry  off 
minute  charges  therefrom. 

A  convective  discharge,  though  often  attended  by  a  feeble 
sound,  is  sometimes  called  a  silent  discharge  in  order  to  dis- 
tinguish it  from  the  noisy,  disruptive  discharge,  which  is  at- 
tended by  a  sharp  snap,  or,  when  considerable,  by  a  loud 
report. 

A  convective  discharge  is  also  called  a  glow  or  brush  dis- 
charge. The  latter  is  best  seen  at  the  small  button  at  the 
end  of  the  prime,,  or  positive  conductor,  of  a  frictional  electric 
machine. 

The  positive  discharge  from  a  point  or  small  rounded  con- 
ductor is  always  brush  shaped  ;  the  negative  discharge  is  al- 
ways star  shaped. 


193  A  DICTIONARY  OF  ELECTRICAL 

In  rarefied  gases,  the  discharge  is  convective  in  character 
and  produces  various  luminous  effects  of  great  beauty,  the 
color  of  which  depends  on  the  kind  of  gas,  and  the  size,  shape, 
and  material  of  electrodes,  and  on  the  degree  of  the  vacuum. 
Thus,  in  the  rarefied  space  of 
the  vessel  shown  in  Fig.  141, 
the  discharge,  becomes  an  ovoidal 
mass  of  light  sometimes  called  the 
Philosopher's  Egg. 

When  the  discharges  in  rarefied 
gases  follow  one  another  very  rap- 
idly, alternations  of  light  and  dark- 
ness, or  stratification,  or  striae  are 
produced. 

The  breadth  of  the  dark  bands 
increases  as  the  vacuum  becomes 
higher.  The  light  portions  start 
at  the  positive  electrode,  and  are 
hotter  than  the  dark  portions. 

The  effects  of  the  luminous  con- 
vective discharge  are  best  seen 
in  exhausted  glass  tubes,  called 
Geissler  Tubes,  containing  residual 
atmospheres  of  various  gases.  (See 
Fig.  lUl.  Geissler  Tubes.) 

Discharge,  Disruptive — The  sudden,  and 

more  or  less  complete,  discharge  that  takes  place  across  an 
intervening  non-conductor  or  dielectric. 

A  mechanical  strain  of  the  dielectric  occurs,  which  sudden- 
ly permits  the  discharge  to  pass  as  a  spark,  or  rapid  succes- 
sion of  sparks. 

In  air,  the  spark,  when  long,  generally  takes  the  zigzag 
path  as  shown  in  Fig.  142. 

These  sparks  consist  of  heated  gases,  and  portions  of  the 
conductor  that  are  volatilized  by  the  heat, 


WORDS,  TERMS  AND  PHRASES.  193 

The  discharge  of  a  Ley  den  jar  or  Condenser,  may  be  dis- 
ruptive, as  when  the  discharging  rod  is  held  with  one  knob  con- 
nected with  one  coating,  and  the  other  near  the  other  coating. 
It  may  be  gradual,  as  when  the  two  coatings  are  alternately 
connected  with  the  ground. 

The  stress  is  often  sufficient  to  pierce  the  glass. 


Fig.  ll#. 

Discharge,  Duration  of The  time  required 

to  effect  a  complete  disruptive  discharge. 

The  disruptive  discharge  is  not  instantaneous ;  some  time 
is  required  to  effect  it.  Estimates  of  the  duration  of  a  flash  of 
lightning,  based  on  the  duration  of  a  Leyden  jar  discharge,  are 
misleading  from  the  enormous  difference  in  the  quantity  and 
the  potential  in  the  two  cases. 

Leyden  jar  discharges,  are,  however,  accomplished  in  very 
small  periods  of  time. 

Discharge  Key. — (See  Key,  Discharge.) 

Discharge,  Lateral (See  Lateral  Discharge.) 

Discharge,  Oscillating A  number  of  suc- 
cessive discharges  and  recharges  which  occur  on  the  disruptive 
discharge  of  a  Leyden  jar,  or  condenser. 

The  disruptive  discharge  of  a  Leyden  jar,  or  condenser,  is 
not  effected  by  a  single  rush  of  electricity.  When  discharged 
through  a  small  resistance,  a  number  of  alternate  partial  dis- 


15*4  A  DICTIONARY  OF  ELECTRICAL 

charges  and  recharges  occur,  which  produce  true  oscillations 
or  undulatory  discharges. 

These  oscillations  are  caused  by  the  induction  of  the  dis- 
charge on  itself,  and  are  similar  to  the  mutual  induction  of  a 
current. 

Discharger,  Universal (See  Universal  Dis- 
charger.) 

Discharging;  Rod  or  Tongs. — Metallic  rods  terminated 
at  one  end  with  balls  and  connected  at  the  other  by  a 
swinging  joint,  and  capable  of  mo- 
tion at  the  free  ends  towards,  or  from, 
one  another;  employed  for  the  dis- 
charge of  Leyden  batteries  or  con- 
densers. 

The  insulated  handles  H,  H,  Fig.  143, 
permit  the  balls  at  M  M  to  be  readily 
applied  to  the  opposite  coatings  of  the 
jar  or  condenser. 

Disconnections.  —  A  term  em- 
ployed to  designate  one  of  the  varieties 

of  faults  caused  by  the  accidental  breaking  or  disconnection 
of  a  circuit. 
Disconnections  of  this  kind  may  be  : 

(1)  Total;  as  by  a  switch  inadvertently  left  open  ;  or  by  the 
accidental  breaking  of  a  part  of  the  circuit. 

(2)  Partial;  as  by  a  dirty  contact;  a  loose,  or  badly  soldered 
joint ;  a  poorly  clamped  binding  screw  ;  a  loose  terminal,  or  a 
bad  earth. 

(3)  Intermittent ;  as  by  swinging  joints;  alternate  expansions 
or  contractions,  on  changes  of  temperature ;  the  collection  of 
dust  and  dirt  in  dry  weather,  and  their  washing  out  in  wet 
weather. 

Dispersion  Photometer.— (See  Photometer,  Disper- 
sion.) 


WORDS,  TERMS  AND  PHRASES.  195 

Dissimulated  or  Latent  Electricity. — The  condition 
of  an  electric  charge  when  placed  near  an  opposite  charge,  as 
in  a  Leyden  jar  or  condenser. 

In  this  case,  merely  touching  one  of  these  charged  surfaces 
will  not  effect  its  complete  discharge.  (See  Bound  and  Free 
Charge.) 

Electricity  in  the  condition  of  a  bound  charge  was  formerly 
called  latent  electricity.  This  term  is  now  in  disuse. 

Dissipation  of  Charge.— The  gradual  but  final  loss  of 
any  charge  by  leakage,  which  occurs  even  in  a  well  insulated 
conductor. 

This  loss  is  more  rapid  with  negatively  charged  conductors, 
than  with  those  positively  charged. 

Crookes,  of  England,  has  retained  a  charge  in  conductors  for 
years,  without  appreciable  leakage,  by  placing  the  conductors 
in  vessels  in  which  a  high  vacuum  was  maintained.  (See 
Vacuum,  High.) 

Dissociation. — The  separation  of  a  chemica  compound 
into  its  elementary  parts  by  the  action  of  heat. 

Distillation,  Dry  or  Destructive The 

action  of  heat  on  an  organic  substance,  while  out  of  contact 
with  air,  as  a  result  of  which  the  substance  is  decomposed  into 
simpler  and  more  stable  compounds. 

The  products  resulting  from  the  decomposition  may  be  suc- 
cessively collected  by  the  ordinary  processes  of  distillation. 

Distillation,  Electric The  distillation  of 

a  liquid  in  which  the  effects  of  heat  are  aided  by  an  electrifica- 
tion of  the  liquid. 

Beccaria  discovered  that  an  electrified  liquid  evaporates 
more  rapidly  than  when  unelectrified. 

Distribution  Box.— (See  Box,  Distribution.) 

Distribution  of  Electric  Charge.  (See  Charge,  Dis- 
tribution of.) 


196  A  DICTIONARY  OF  ELECTRICAL 

Distribution  of  Electricity,  Systems  of.— (See  Sys- 
tems  of  Distribution  by  Alternating  Currents; — by  Direct 
Currents.) 

Door-Opener,  Electric A  device  for  open- 
ing a  door  from  a  distance  by  electricity. 

Various  devices  consisting  of  electro-magnets,  acting  against, 
or  controlling,  springs  or  weights,  are  employed  for  this 
purpose. 

Double-Carbon  Arc  Lamp. — An  electric  arc  lamp 
provided  with  two  pairs  of  carbon  electrodes,  so  arranged, 
that  when  one  j>air  is  consumed,  the  circuit  is  automatically 
completed  through  the  other  pair. 

Double-Contact  Key. — (See  Key,  Double- Contact.) 

Double-Current,  or  Reverse  Current  Working. 
— The  employment,  in  systems  of  telegraphy,  by  means  of 
suitable  keys,  of  currents  from  voltaic  batteries,  in  alternately 
opposite  directions  thus  increasing  the  speed  of  signaling. 

Double  -  Fluid  Electrical  Hypothesis.— (See  Elec- 
tricity, Hypothesis  of.) 

Double-Fluid  Voltaic  Cells.— (See  Voltaic  Cells.) 

Double-Refraction.— (See  Refraction,  Double.) 

Double-Refraction,  Electric (See  Electric, 

Double  Refraction.) 

Double-Touch,  Magnetization  by A 

method  for  producing  magnetization  by  the  simultaneous 
touch  of  two  magnet  poles.  (See  Magnetization,  Methods  of. ) 

Doubler  of  Electricity.— An  early  form  of  continuous 
elctrophorus.  (See  Electrophorus.) 

Drill,  Electro-magnetic  — A  drill,  applied 

especially  to  blasting  or  mining  operations,  operated  by 
means  of  electricity. 

Drum,  Electro-magnetic A  drum,  used  in  feats 

of  legerdemain,  operated  by  an  automatic  electro-magnetic 
make  and  break  apparatus. 


WORDS,  TERMS  AND  PHRASES.  197 

Drum  or  Cylinder  Armature.— An  armature  for  a 
dynamo-electric  machine,  in  which  the  coils  are  wrapped 
around  the  outside  of  a  hollow  cylindrical  or  drum-shaped 
core.  (See  Dynamo-Electric  Machine,  Armatures  of.) 

Dry  Pile.— A  voltaic  pile  or  battery  consisting  of  numerous 
cells,  the  voltaic  couple  in  each  of  which  consists  of  sheets  of 
paper  covered  with  zinc-foil  on  one  side,  and  black  oxide  of 
manganese  on  the  other. 

Various  modifications  of  the  above  are  possible. 

Duplex  Telegraphy. — Devices  by  means  of  which  two 
messages  can  be  simultaneously  sent  over  a  single  wire,  in 
opposite  directions.  (See  Telegraphy,  Duplex.) 

Duration  of  Electric  Discharge. — (See  Discharge, 
Duration  of.) 

Dyad. — A  dyad  or  "bivalent  element,  is  one  which  has  two 
bonds  by  which  it  can  unite  or  combine  with  another  element. 

An  element  whose  atomicity  is  bivalent. 

Dyeing,  Electric The  application  of  electricity 

to  the  reduction,  or  the  oxidation,  of  the  aniline  salts  used  in 
dyeing. 

Goppelsroder,  in  his  processes  of  electro-dyeing,  forms  and 
fixes  aniline  black  on  cloths  as  follows;  viz.,  the  cloth,  satu- 
rated with  aniline  salt,  is  placed  on  an  insulated  metallic 
plate,  inert  to  the  aniline  salt,  and  connected  with  one  pole 
of  a  battery  or  other  electric  source.  The  other  pole  is  con- 
nected with  a  metallic  plate  on  which  the  required  design  is 
drawn.  On  the  passage  of  the  current,  the  design  is  traced  in 
aniline  black  on  the  cloth.  A  minute  or  two  suffices  for  the 
operation. 

A  species  of  electrolytic  writing  is  obtained  on  cloths  ar- 
ranged as  above  by  substituting  a  carbon  pencil  for  the  metallic 
plate.  On  writing  with  this  pencil,  as  with  an  ordinary  pencil, 
the  passage  of  the  current  so  directed,  is  followed  by  the  de- 
position of  aniline  black. 


198  A  bICTIONARY  OF  ELECf RlCAL 

By  means  of  a  somewhat  similar  process  writing  in  white 
on  a  colored  ground  is  obtained. 

Dynamic  Attraction. — (See  Attraction,  Dynamic.) 
Dynamic  Electricity.— A  term  formerly  employed  for 
current  electricity.    Now  going  out  of  use. 

Dynamic§,  Electro (See  Electro  Dynamics.) 

Dynamo  Battery.— (See  Battery,  Dynamo. ) 
Dynamo-Electric  Machine. — A  machine  for  the  con- 
version of  mechanical  energy  into  electrical  energy,  by  means 
of  electro-magnetic  induction. 

The  term  is  also  applied  to  a  machine  by  means  of  which 
electrical  energy  is  converted  into  mechanical  energy  by  means 
of  electro-magnetic  induction.  Machines  of  the  latter  class, 
are  generally  called  motors,  those  of  the  former,  generators. 

A  dynamo-electric  generator,  or  a  dynamo-electric  machine 
proper,  consists  of  the  following  parts,  viz.  : 

(1)  The  revolving  portion,  usually  the  Armaturejin  which  the 
electro-motive  force  is  developed,  which  produces  the  current. 

It  must  be  borne  in  mind  that  it  is  not  current  but  differ- 
ences of  electric  potential,  or  electro-motive  forces,  that  are  de- 
veloped by  any  electric  source  from  which  a  current  is  obtained. 
For  ease  of  reference,  however,  we  will  speak  of  an  electric  cur- 
rent as  being  generated  by  the  armature,  or  source.  No  ambig- 
uity will  be  introduced  if  the  student  bears  the  above  in  mind. 

(2)  The  Field  Magnets,  which  produce  the  field  in  which  the 
armature  revolves. 

(3)  The  Pole  Pieces,  or  free  terminals  of  the  field  magnets. 

(4)  The  Commutator,  by  which  the  currents  developed  in  the 
armature  are  caused  to  flow  in  one  and  the  same  direction.   In 
alternating  machines  and  some  continuous  current  dynamos 
this  part  is  called  the  Collector. 

(5)  The   Collecting  Brushes,  that  rest  on  the  Commutator 
Cylinder  and  take  off  the  current  generated  in  the  armature. 

Dynamo-Electric  Machine,  Armature.— The  coils 
of  insulated  wire  and  the  iron  core  on  or  around  which  the  coils 
are  wound. 


WORDS,  TERMS  AND  PHRASES. 


199 


Fig.  VtU. 


Armatures  are  generally  divided  into  the  following  classes, 
viz.  : 

(1)  Ring-Armatures,  in  which  the  armature  coils  are  wound 
around  a  ring  shaped  core,  as  shown  in  Fig.  144. 

(2)  Drum- A  r  in  a- 
tures,  in  which  the 
armature    coils    are 
wound    longitudi- 
nally over  the  sur- 
face of  a  cylinder  or 
drum,  as  shown  in 
Fig.  145. 

(3)  Pole  or  Radial- 
Armatures,  in  which 

the  armature  coils  are  wound  on  separate  poles  that  project 

radially  from  the  periphery  of  a  disc,  as  shown  in  Fig.  146. 

(4)  Disc  Armatures, 
in  which  flat  coils  are 
supported  on  the  sur- 
face of  a  disc. 

Dynamos  are  some- 
times divided  into  Uni- 
polar, Bipolar  and  Mul- 
tipolar.  A  unipolar- 
armature  is  one  whose 
polarity  is  never  re- 
versed. A  bipolar- 
armature  is  one  in 
which  the  polarity  is 
Fig.  ikt.  reversed  twice  in  every 

rotation ;  multipolar-armatures  have  their  polarity  reversed  a 

number  of  times  in  every  rotation. 

Dynamo-Electric  machine,  Armature  Coils.— The 
coils,  strips  or  bars  that  are  wound  on  the  armature  core. 
To  avoid  needless  resistance  the  wire  should  be  as  short 


500  A  DICTIONARY  OF  ELECTRICAL 

and  thick  as  will  enable  the  desired  current  to  be  obtained 
without  excessive  speed  of  rotation. 

The  armature  coils  should  enclose  as  many  line.s  of  force  as 
possible  (i.  e.,  they  should  have  as  nearly  a  circular  outline  as 
possible).  In  drum-armatures,  the  breadth  should  nearly  equal 
the  length,  unless  other  considerations  prevent. 


When  the  armature  wire  consists  of  rods  or  bars,  it  should 
be  laminated  or  slit  in  planes  perpendicular  to  the  lines  of 
force  so  as  to  avoid  eddy  currents.  The  greater  the  number 
of  coils,  other  things  being  equal,  the  more  uniform  the  cur- 
rent generated.  The  separate  coils  should  be  symmetrically 
disposed,  otherwise  irregular  induction,  and  consequent  spark- 
ing at  the  commutator  results. 

The  coils  of  pole-armatures  should  be  wound  near  th'e  poles 
rather  than  on  the  middle  of  the  cores.  In  order  to  avoid  undue 
heating,  spaces  for  air  ventilation  are  not  inadvisable.  Vari- 
ous connections  of  the  armature  coils  are  used. 

In  some  machines  all  the  coils  are  connected  in  a  closed  cir- 
cuit. In  some,  the  coils  are  independent  of  one  another,  and, 
either  for  the  entire  revolution,  or  for  a  part  of  a  revolution, 
are  on  an  open  circuit. 

In  alternating  current  dynamos  in  order  to  obtain  the  rapid 
reversals  or  alternations  of  current,  whieh  in  some  machines 


WORDS,  TERMS  AND  PHRASES. 


201 


are  as  high  at  12,000  per  minute,  a  number  of  poles  of  alternate 
polarity  are  employed.  The  separate  coils  that  are  used  on 
the  armature  may  be  coupled  either  in  series  or  in  mul- 
tiple-arc. 

Where  a  comparatively 
low  electro-motive  force  is 
sufficient,  such  as  for  incan- 
descent lamps  in  multiple- 
arc,  the  separate  coils  are 
united  in  parallel;  but  for 
purposes  where  a  consider- 
able electro-motive  force  is 
necessary,  as,  for  example, 
in  systems  of  alternate  cur- 
rent distribution,  with  con- 
verters at  considerable  dis- 
tances from  the  generating, 
alternating  current  dynamo,  they  are  often  connected  in 
series,  as  shown  in  the  Fig.  147. 

Dynamo-Electric    Machine,    Armature     Core.— 

The  iron  core,  on,  or  around  which,  the  armature  coils  are 
wound. 

The  armature  core  is  laminated  for  the  purpose  of  avoiding 
the  formation  of  eddy  currents. 

In  drum,  and  in  ring-armatures,  the  laminaa  should  be  in  the 
form  of  thin  insulated  discs  or  plates  of  soft  iron  ;  in  pole-arma- 
tures they  should  be  in  the  form  of  bundles  of  insulated  wires. 

The  iron  in  the  coi'es  should  be  of  such  an  area  of  cross 
section,  as  not  to  be  readily  oversaturated. 

Dynamo-Electric  Machine,  Cause  of  Current 
generated  by The  current  developed  in  the  arma- 
ture coils  is  due  to  the  cutting  of  the  lines  of  magnetic  force 
of  the  field  by  the  coils  during  the  rotation  of  the  armature. 

If  a  loop  of  wire,  whose  ends  are  connected  to  the  two-part 


A  DICTIONARY  OF  ELECTRICAL 


commutator,  shown  in  Fig.  148,  be  rotated  in  the  magnetic 
field  between  the  magnet  poles  N  and  S,  in  the  direction  of  the 

large  arrow,  cur- 
rents will  be  gen- 
erated which  will 
flow  in  the  direc- 
g  tion  indicated  by 
the  small  arrows 
during  its  motion 
past  the  north 
Fig.  llS.  pole  from  the  top 

to  the  bottom,  but  in  the  opposite  direction  during  its  motion 
past  the  south  pole,  from  the  bottom  to  the  top.  If  now  the 
brushes  rest  on  the  com- 
mutator in  the  position 
shown  in  the  Fig.  149,  the 
vertical  line  of  the  gap 
between  the  poles  corre- 
sponding with  the  vertical 
gap  between  the  commu- 
tator segments,  the  cur- 
rents generated  in  the  loop 
will  be  caused  to  flow  in  one  and  the  same  direction,  and 
B'  will  become  the  positive  brush  since  the  end  of  the 

loop  is  connected  wit}*  it 
only  so  long  as  it  is  posi- 
tive. As  soon  as  it  becomes 
negative,  from  the  current 
in  the  loop  flowing  in  the 
opposite  direction,  the 
other  end,  which  is  then 
positive,  is  connected  with 
the  positive  brush. 
Fig.  150.  A  similar  series  of 

changes  occur  at  the  negative  brush,  B. 
Theoretically,  the  neutral  points,  where  the  brushes  rest, 


WORDS,  TERMS  AND  iPHRASES.  208 

would  be  in  the  vertical  line  coinciding  with  that  of  the  gap 
between  the  poles.  An  inspection  of  the  figure  shows  that 
the  Neutral  Line,  or  the  Diameter  of  Commutation,  is  dis- 
placed in  the  direction  of  rotation.  (See  Diameter  of  Com- 
mutation). The  displacement  of  the  brushes,  so  necessitated, 
is  called  the  lead.  The  cause  of  the  lead  is  the  reaction  that 
occurs  between  the  magnetic  poles  of  the  field  magnets  and 
those  of  the  armature,  the  result  of  which  is  to  displace  the 
field  magnet  poles,  and  to  cause  a  change  in  the  density  in  the 
field.  This  is  shown  in  Fig.  150,  where  the  density  of  the  lines 
of  force  indicates  the  position  of  the  diameter  of  commutation 
as  being  near  n  s,  or  at  right  angles  to  the  diameter  of  greatest 
average  magnetic  density.  The  magnetic  lag  also  influences 
the  positive  of  the  neutral  line.  (See  Lead.  Angle  of  Lag.) 

Dynamo-Electric  machine,  Collecting  Brushes. 
— Metallic  brushes  which  bear  on  the  commutator  cylinder, 
and  take  off  the  current  generated  by  the  difference  of  poten- 
tial in  the  armature  coils.  (See  Brushes,  Collecting.) 

Dynamo-Electric  machine,  Commutator.— The 
part  of  a  dynamo-electric  machine  which  is  designed  to  cause 
the  alternating  currents  produced  in  the  armature  to  flow  in 
one  and  the  same  direction  in  the  external  circuit. 


Rf 

Fig.  151.  Fig.  152. 

The  character  of  the  commutator  depends  on  the  shape, 
arrangement,  and  number  of  armature  coils,  and  on  the 
character  of  the  magnetic  field. 


204 


A  DICTIONARY  OF  ELECTRICAL 


In  action,  the  commutator  is  subject  to  wear  from  the  friction 
of  the  brushes,  and  the  burning  action  of  destructive  sparks. 
The  commutator  segments  are,  therefore,  made  of  compara- 
tively thick  pieces  of  metal,  insulated  from  one  another,  and 
supported  on  a  commutator  cylinder  usually  placed  on  the 
shaft  of  the  armature. 

The  enJs  of  the  armature  coils  are  connected  to  commuta- 
tor strips  or  segments. 


Fig.  153.  fig.  151.. 

Figs.  151,  152,  and  153,  show  the  connections  of  an  arma- 
ture coil  to  the  plates  of  a  two-part  commutator.  (See  Com- 
mutator.} 

The  connections  of  a  four-part  commutator  for  a  ring  arma- 
ture, and  the  connections  of  the  coils  are  shown  in  the  an- 
nexed Fig.  154. 

The  commutator  strips  may  either  connect  the  separate 
coils  in  one  closed  circuit,  in  which  the  coils  are  all  connected 
with  one  another,  or,  in  an  open  circuited  armature,  the 
separate  coils  are  independent  of  one  another. 

Dynamo-Electric  machine,  Field  magnets.— The 
electro  magnets  employed  to  produce  the  magnetic  field  of  a 
dynamo-electric  machine. 


WORDS,  TERM  S   AND  PHRASES. 


205 


The  field  magnets  consist  of  a  suitable  frame,  or  core,  on 
which  the  field  magnet  coils  are  wound. 

The  field  magnet  cores  are  made  of  thick  and  solid  iron,  as 
soft  as  possible.  They  should  contain  plenty  of  iron  in  order 
to  avoid  too  ready  magnetic  saturation. 

All  edges  and  corners  are  to  be  avoided,  since  they  tend  to 
cause  an  irregular  distribution  of  the  field. 


Fig.  155. 


Fig.  156. 


The  field  magnets  should  have  sufficient  magnetic  strength 
to  prevent  the  magnetizing  effect  of  the  armature  from 
unduly  influencing  the  field,  and  thus,  by  causing  too  great  a 
lead,  produce  injurious  sparJcing. 

Dynamo-Electric  Machine,  methods  of  Increas- 
ing the  Electro-motive  Force  generated  by 

The  electro-motive  force  of  a  dynamo-electric  machine  may 
be  increased  in  the  following  ways,  viz.: 


A  DICTIONARY  OF  ELECTRICAL 


(1)  By  increasing  its  Speed  of  Rotation. 

(2)  By  increasing  the  Strength  of  the  Magnetic  Field  be- 
tween which  the  armature  rotates. 

(3)  By  increasing  the  Size  of  the  Field  through  which  the 
armature  passes  in  unit  time,  the  intensity  remaining  the  same. 

(4)  By  increasing  the  Number  of  Armature  Windings,  i.  e., 
by  making  successive  parts  of  the  same  wire  pass  simultane- 
ously through  the  field. 

(5)  By  increasing  the  Number  of  Fields  passed  through  by 
the  same  wire. 

Dynamo-Electric  Machine,  Pole  Pieces.—  Massive 

pieces  of  iron  placed  on 
the  poles  of  the  field  mag- 
nets of  dynamo-electric 
machines,  to  define  and 
limit  the  magnetic  field. 
The  pole  pieces  should 
be  of  massive,  soft  iron. 
They  are  sometimes 


are 

laminated  so  as  to  avoid 
eddy  currents.  When  de- 
signed to  produce  a  uni- 
form field  they  must  ex- 
tend on  each  side  of  the 
armature,  but  not  too  far, 
else  a  loss  will  be  occa- 
sioned by  the  lines  of 
|r  magnetic  force  closing 
directly  through  the 
Fig.  157.  edges  of  the  opposite  pole 

pieces,  instead  of  through  the  armature. 

Dynamo-Electric  Machines,  Compound  Wound 
---  Machines  whose  field  magnets  are  excited  by  more 
than  one  circuit  of  coils,  or  by  more  than  a  single  electric 
source. 
Compound  dynamos  are  of  two  classes,  viz.: 


WORDS.  TERMS  AND  PHRASES. 


207 


(1)  Those  designed  to  produce  a  Constant  Potential,  and 

(2)  Those  designed  to  produce  a  Constant  Current. 
For  Constant  Potential. 

The  combination  of  a  Series  and  Separately  Excited  ma- 
chine is  shown  in  Fig.  155.  The  field  is  in  series  with  the 
armature,  but  has  also  an  additional  and  separate  excita- 
tion. 

The  combination  of  a 
Series  and  Shunt  machine 
ensures  the  excitation  of 
the  field  both  by  the  main 
and  by  a  shunted  current. 
Such  a  combination  is 
shown  in  Fig.  156. 

For  Constant  Current. 

The  combination  of 
shunt  and  separately  ex- 
cited machine  is  shown  in 
Fig.  157.  In  this  machine 
the  field  is  excited  by 
means  of  a  shunt  to  the 
external  circuit,  and  by  a 
current  produced  by  a  sep- 
arate source. 

The  combination  of  a 
Series  and  Magneto  Ma- 


Fig.  158. 


chine  is  shown  in  Fig.  159.     This,  also,  is  designed  to  give  a 
constant  current. 
Dynamo-Electric  Machines,  Varieties  of 

Dynamo-electric  machines  may  be  divided  into  different 
classes  according  to  the  manner  in  which  their  field  mag- 
nets are  excited. 

In  a  Series  Dynamo,  Fig.  159,  the  armature  circuit  is  con- 
nected in  series  with  the  field  circuit;  therefore  the  entire  arm- 
ature current  must  pass  through  the  field  coils. 


208  A  DICTIONARY  OF  ELECTRICAL 

In  a  Shunt  Dynamo,  Fig.  160,  the  field  magnet  coils  are 
placed  in  a  shunt  to  the  external  circuit,  so  that  only  a  por- 
tion of  the  current  generated  in  the  armature  passes  through 
the  field  magnet  coils,  but  all  the  difference  of  potential  of  the 
armature  acts  at  the  terminals  of  the  field  circuit. 

In  a  Separately  Excited  Dynamo,  Fig.  161,  the  field  magnet 
coils  have  no  connection  with  the  armature  coils,  but  receive 
their  current  from  a  separate  machine  or  source. 


D     D     D     D 

H  Fig.  ICO. 

The  Magneto-Electric  machine,  Fig.  162,  has  no  field  magnet 
coils,  its  field  being  due  to  permanent  steel  magnets. 

The  author  has  collated  the  above  on  dynamo-electric 
machines  largely  from  S.  P.  Thompson's  admirable  book  on 
"  Dynamo-Electric  Machinery,"  third  edition,  to  which  the  stu- 
dent is  referred  for  further  particulars  of  construction  or 


WORDS,  TERMS  AND  PHRASES. 


209 


operation.     He  is  also  indebted  to  Bering's  "Principles  of 
Dynamo-Electric  Machines." 

Dynamograph.—  A  term  sometimes  applied  to  a  type- 
writing telegraph  that  records  the  message  in  type-  written 
characters,  both  at  the  sending  and  the  receiving  ends. 

Dynamometer.—  A  name 
given  to  a  variety  of  appara- 
tus for  measuring  the  power 
of  an  engine  or  motor. 

In  all  dynamometers,  the 
stress  on  the  belt,  or  other 
moving  part,  is  measured,  say 
in  pounds,  and  the  speed  of 
the  moving  part  is  also  meas- 
ured in  feet  per  second.  The 
product  of  the  strain  in  pounds 
by  the  velocity  in  feet  per 
second,  divided  by  550,  will 
give  the  horse  power. 

One  of  the  many  forms  of 
dynamometers  is  shown  in 
Fig.  163.  It  is  known  as  Par- 
sons' Dynamometer.  fig.  iei. 

The  driving  pulley  is  shown  at  A,  and  the  driven  pulley  at 
C.  Weights  hung  at  Q  are  varied  so  as  to  maintain  the  axes 
of  the  suspended  pulleys,  D  and  B,  as  nearly  as  possible  at  the 
same  height.  Then  the  tension  Tx  and  T2,  of  the  sides  O  and 
O',  of  the  belts,  will  be  represented  by  the  following  equation  : 

P  —  Q 
T2  —  T!  =  —  g  —  ,  from  which,  knowing  the  belt  speed,  the 

horse  power  may  be  deduced. 

Dynamometer,  Electro  -  -—A  form  of  galvan- 
ometer for  the  measurement  of  electric  currents, 


210 


A  DICTIONARY  OF  ELECTRICAL 


In  Siemens'  Electro  Dynamometer,  shown  in  Fig.  164, 
there  are  two  coils ;  a  fixed  coil  C,  secured  to  an  upright  sup- 
port, and  a  movable  coil  D  .consisting  often  of  but  a  single  turn 
of  wire.  The  movable  coil  is  suspended  by  means  of  a  thread 
and  a  delicate  spring  S,  capable  of  being  twisted  by  turning 
a  milled  screw-head  through  an  angle  of  torsion  measured 
on  a  scale  by  means  of  an  index  connected  to  the  screw-head. 
The  two  ends  of  the  movable  coil  dip  into  mercury  cups  so 
connected  that  the  current  to  be  measured  passes  through  the 
fixed  and  movable  coils  in  series. 

When  ready  for  use,  the  movable 
coil  is  at  right  angles  to  the  fixed  coil. 
The  current  to  be  measured  is  then 
sent  into  the  coils,  and  their  mutual 
action  tends  to  place  the  movable  coil 
parallel  to  the  fixed  coil  against  the 
torsion  of  the  spring  S.  The  amount 
of  this  force  can  be  ascertained  by  de- 
termining the  amount  of  torsion  re- 
quired to  bring  the  movable  coil  back 
to  its  zero  position. 

Since  the  same  current  passes  through 
both  the  fixed  and  movable  coils,  and 
they  both  act  on  each  other,  the  deflect- 
ing force  here  is  evidently  proportional  to  the  square  of  the 
strength  of  the  current  to  be  measured.  The  deflecting  force, 
and  consequently  the  current  strength,  is  therefore  propor- 
tional to  the  square  root  of  the  angle  of  torsion,  and  not  di- 
rectly to  the  angle  of  torsion. 

Dyne.— The  unit  of  force. 

The  force  which  in  one  second  can  impart  a  velocity  of  one 
centimetre  per  second  to  a  mass  of  one  gramme. 

Earth  Circuit  or  Ground  Circuit.— (See  Circuit, 
Grounded.) 


Fig.  162. 


WORDS,  TERMS  AND  PHRASES. 


211 


Earth  Currents. — Electric  currents  flowing  through 
different  parts  of  the  earth  caused  by  a  difference  of  potential 
at  different  parts. 

The  causes  of  these  differences  of  potential  are  various. 

Earth,  Dead  or  Solid 

—(See  Earths.} 

Earth  or  Ground.— The  earth 
or  ground  which  forms  part  of  an 
electric  circuit. 

A  circuit  is  put.  to  earth  or  ground 
when  {lie  earth  is  used  for  a  portion 
of  the  circuit. 

The  resistance  of  an  earth  con- 
nection may  vary  in  time  from  the 
following  causes,  viz. : 

(1)  The    corrosion  of    the  plate. 
This  is  especially  apt  to  occur  in 
the  case  of  a  copper  plate. 

(2)  From  polarization,  a  counter 
electro-motive  force  being  produced , 
thus  introducing  a  spurious  resist- 
ance.   (See  Spurious  Resistance.) 

Earth,  Partial (See 

Earths.) 

Earth,  Swinging (See 

Earthf.) 

Earths.— Faults  in  telegraph  or 
other  lines  caused  by  accidental  con- 
tact of  line  with  the  ground  or 
earth. 

Earths  are  of  three  kinds,  viz. :  Fig- 163. 

(1)  Total,  or  Dead  Earth,  where  the  wire  is  thoroughly 
grounded  or  connected  with  the  earth. 

(2)  Partial  Earth,  or  where  the  wire  is  in  imperfect  con- 
nection  with  the  earth, 


212 


A  DICTIONARY  OP  ELECTRICAL 


(3)  Intermittent  Earth,  or  when  the  wire  makes  intermittent 
contact  with  the  earth  by  the  action  of  the  wind,  or  by 
occasional  expansion  by  heat. 

Ebonite  or  Vulcanite. — A  black  variety  of  hard  rubber 
which  possesses  high  powers  of  insulation  and  specific  induc- 
tive capacity. 


Vulcanite  rubbed  with  cat-skin  acts  as  one  of  the  best  known 
substances  for  becoming  electrified  by  friction.  For  this  pur- 
pose it  should  be  thoroughly  dried, 


WORDS,  TERMS  AND  PHRASES. 


213 


Economic  Coefficient,  or  Efficiency  of  a  Dynamo. 

— (See  Coefficient,  Economic,  of  a  Dynamo.} 

Effect,  Edison  —  —An  electric  discharge  between 
one  of  the  terminals  of  the  incandescent  filament  of  the  elec- 
tric lamp,  and  a  metallic  plate  placed  near  the  filament  but 
disconnected  therefrom,  as  soon  as  a  certain  difference  of  po- 
tential is  reached  between  the  lamp  terminals. 

The  effect  of  the  discharge  is  to  produce  a  current  in  a 
circuit  connected  to  one  pole  of  the  lamp  terminals  and  the 
metallic  plate,  as  may  be 
shown  by  means  of  a  gal- 
vanometer. 

Effect,   Hall  

— An  effect  produced  by  I 
placing  a  very  thin  me- 
tallic strip,  conveying  an 
electric  current,  in  a 
strong  magnetic  field. 

The  cross  ABC  I),  Fig. 
1G5,  is  cut  out  of  a  gold 
leaf  or  other  very  thin 
metallic  sheet.  The  ends 
A  and  B  are  connected 
with  the  terminals  of  a 
battery  S,  and  C  and  D 
with  the  galvanometer  G. 

None  of  the  battery  current  can  therefore  flow  through  the 

alvanometer. 

If,  now,  the  metallic  cross  be  placed  in  a  powerful  magnetic 
field,  the  lines  of  force  of  which  are  perpendicular  to  the  plane 
of  the  cross,  the  deflection  of  the  galvanometer  needle  will 
show  the  existence  of  a  current,  which,  if  the  battery  current 
flows  in  the  direction  of  the  arrow,  or  from  A  to  B,  if  the  lines 
of  magnetic  force  pass  through  the  leaf  from  the  front  to  the 
back  of  the  sheet,  when  the  cross  is  formed  of  gold,  silver, 


214  A  DICTIONARY  OP  ELECTRICAL 

platinum  or  tin-foil,  will  flow  through  C  D,  from  C  to  D,  but  in 
the  opposite  direction  if  formed  of  iron.  These  effects  cease 
if  the  conductor  is  increased  in  thickness  beyond  a  certain 
extent. 

Effect,  Joule A  term  applied  to  the  heat  de- 
veloped in  a  conductor  by  the  passage  through  it  of  an  elec- 
tric current. 

The  rate  at  which  this  occurs  is  proportional  to  the  resist- 
ance of  the  conductor  multiplied  by  the  square  of  the  current. 
(See  Heat,  Electric.) 

Effect,  Peltier The  heating  effect  produced  by 

the  passage  of  an  electric  current  across  a  thermo-electric  junc- 
tion. (See  Junction,  Thermo-Electric.) 

The  passage  of  the  current  across  a  thermo-electric  junction 
produces  either  heat,  or  cold.  If  heat  is  produced  by  its 
passage  in  one  direction,  cold  is  produced  by  its  passage  in  the 
opposite  direction.  The  Peltier  effect  may,  therefore,  mask 
the  Joule  effect. 

The  Peltier  effect  is  therefore  the  converse  of  the  thermo- 
electro  effect,  where  the  uneqal  heating  of  metallic  junctions 
produces  an  electric  current.  (See  Effect,  Joule ;  Effect, 
Thomson.) 

The  quantity  of  heat  absorbed  or  emitted  by  the  Peltier 
effect  is  proportional  to  the  current  strength,  and  not,  as  in 
the  Joule  effect,  to  the  square  of  the  current. 

Effect,     Photo- Voltaic (See     Photo-Voltaic 

Effect.    Selenium  Cell.) 

Effect,  Thomson A  term  applied  to  the  increase 

or  decrease  in  the  differences  of  temperature  is  an  unequally 
heated  conductor,  produced  by  the  passage  of  an  electrical 
current  through  the  conductor. 

The  effects  vary  according  to  whether  the  current  passes 
from  a  colder  to  a  hotter  part  of  the  wire,  or  the  reverse. 

These  effects  differ  in    direction  in  different   metals,  and 


WORDS,  TERMS  AND  PHRASES.  215 

are  absent  in  lead.  Thomson  has  pointed  out  the  similarity 
between  this  species  of  thermo-electric  phenomena,  and 
convection  by  heat,  or  the  phenomena  of  a  liquid  circulating 
in  a  closed  rectangular  tube,  under  the  influence  of  difference 
of  temperature,  in  which  the  heated  fluid  gives  out  heat  iri  the 
cooler  parts  of  the  circuit,  and  takes  in  heat  in  the  warmer 
parts.  This  would  presuppose  that  positive  electricity  carries 
heat  in  copper  like  a  real  fluid,  but  that  in  iron  it  acts  as  though 
its  specific  heat  were  a  negative  quantity,  in  which  respect  it 
is  unlike  a  true  fluid. 

"We  may  express"  says  Maxwell  "both  the  Pel  tier  and  the 
Thomson  effects  by  stating  that  when  an  electric  current  is 
flowing  from  places  of  smaller  to  places  of  greater  thermo- 
electric power,  heat  is  absorbed,  and  when  it  is  flowing  in  the 
reverse  direction  heat  is  generated,  and  this  whether  the  dif- 
ference of  thermo-electric  power  in  the  two  places  arises  from 
a  difference  in  the  nature  of  the  metal,  or  from  a  difference  of 
temperature  in  the  same  metal." 

Efficiency  of  Conversion  of  Dynamo The 

total  electric  energy  developed  by  a  dynamo,  divided  by 
the  total  mechanical  energy  required  to  drive  the  dynamo. 
(See  Coefficient,  Economic,  of  Dynamo.) 

Efficiency  of  Dynamo.— (See  Coefficient,  Economic  of 
Dynamo.) 

Efflorescence. — The  crystallization  of  a  salt,  above  the 
line  of  liquid,  on  the  surface  of  a  vessel  containing  a  saline 
solution. 

The  liquid,  by  capillarity  in  a  porous  vessel,  or  by  adhe- 
sion in  an  impervious  vessel,  rises  above  the  level  of  the  main 
liquid  line  and,  evaporating,  deposits  crystals  on  the  vessel. 

This  process  is  technically  called  creeping,  and  is  often  the 
cause  of  much  annoyance  in  voltaic  cells. 

Egg,  Philosopher's (See  Discharge,  Convective.) 

Electric  Absorption.— (See  Absorption,  Electric.) 


216  A  DICTIONARY  OP  ELECTRICAL 

Electric  Alarm.— (See  Alarm,  Electric.} 
Electric  Amalgam.— (See  Amalgam,  Electric.) 
Electric  Analysis.— (See  Analysis,  Electric.} 
Electric  Annealing.— A  process  for  annealing  metals, 
in  which  electric  heating  is  substituted  for  ordinary  heating. 
Electric  Battery.— (See  Battery,  Electric.) 
Electric  Bla§ting.— (See  Blasting,  Electric.) 
Electric  Bleaching.— (See  Bleaching,  Electric.) 
Electric  Blow-Pipe.— (See  Blow-Pipe.  Electric.) 
Electric  Boat.— (See  Boat,  Electric.) 
Electric  Bobbin.— (See  Bobbin,  Electric.) 
Electric   Body   Protector.  —  (See   Body   Protector, 
Electric.) 

Electric  Boiler  Feed.— (See  Boiler  Feed,  Electric.) 
Electric  Bridge. — (See  Bridge,  Electric.) 
Electric  Buoy.— (See  Buoy,  Electric.) 
Electric  Burner.— (See  Burner,  Electric.) 
Electric  Buzzer. — (See  Buzzer,  Electric.) 
Electric  Calorimeter.— (See  Calorimeter,  Electric.) 
Electric  Cautery. — (See  Cautery,  Electric.) 
Electric  Charge.— (See  Charge,  Electric.) 
Electric  Chimes.— (See  Chimes,  Electric.) 
Electric  Chronograph. — (See  Chronograph,  Electric.) 
Electric  Chronoscope. — (See  Chronoscope,  Electric.) 
Electric  Clepsydra.— (See  Clepsydra,  Electric.) 
Electric  Clock.— (See  Clock,  Electric.) 
Electric  Coil.— (See  Coil,  Electric.) 
Electric  Column. — (See  Column,  Electric.) 
Electrically  Controlled   Clock.— (See   Clock,    Con- 
trolled.) 


WORDS,  TERMS  AND  PHRASES.  21  tf 

Electric  Controlling  Clock.— (See  Clock,  Controlling.) 
Electric  Convection  of  Heat.— (See   Convection  of 
Heat,  Electric.) 

Electric  Cords.— (See  Cords,  Electric.) 
Electric  Counter.— (See  Counter,  Electric.) 
Electric  Cross. — (See  Cross,  Electric.) 
Electric  Crucible.— (See  Crucible,  Electric.) 
Electric  Current.— (See  Current,  Electric.) 
Electric  Decomposition. — (See  Decomposition,   Elec- 
tric.) 

Electric  Deposition. — (See  Deposition,  Electric.) 
Electric  Distillation.— (See  Distillation,  Electric.) 
Electric  Double  Refraction.— The  transient  or  mo- 
mentary power  of  double  refraction,  ac- 
quired by  a  transparent  substance  when 
placed  in  an  electric  field.     (See  Refrac- 
tion, Double.) 

The  intensity  of  the  double  refraction  is 
proportional  to  the  square  of  the  electric 
force. 

This  action  is  due  to  the  strain  caused 
by  the  electrostatic  stress  produced  by  the 
field.  A  similar  transient  power  of  double 
refraction  is  acquired  by  many  transparent 
bodies  when  subjected  to  simple  mechan- 
ical stress. 

Electric  Dyeing.— (See  Dyeing, 
Electric.) 

Electric  Dynamometer,  Siemens'. 

— (See  Dynamometer,  Electro.)  pia  iee 

Electric  Eel  (Oymnotus  electricus.)—An  eel  possessing 
the  power  of  giving  powerful  electric  shocks. 


21$  A  DICTIONARY  OF  ELECTRICAL 

The  electricity  is  produced  by  an  organ  extending  the  entire 
length  of  the  body. 

According  to  Faraday,  the  shock  given  by  a  specimen  of  the 
animal  examined  by  him  was  equal  to  that  of  15  Leyden  jars, 
having  a  total  surface  of  25  square  feet.  Fig.  166  shows  the 
general  appearance  of  the  animal. 

Electric  Energy.— (See  Energy,  Electric.') 
Electric  Entropy.— (See  Entropy,  Electric.} 
Electric  Escape.— (See  Escape,  Electric.} 
Electric  Etching.— (See  Etching,  Electric.} 
Electric  Excitability  of  Nerve  Fibre.— (See  Excita- 
bility of  Nerve  Fibre.} 

Electric  Expansion.— (See  Expansion,  Electric.} 
Electric  Explorer. — (See  Explorer,  Electric.} 
Electric  Field.— A  field  of  force,  traversed  by  imagin 
ary  lines  of  force  somewhat  similar  to  the  magnetic  field. 
(See  Field,  Electric.} 

Electric  Figures,  Breath.— (See  Figures,  Electric, 
Breath.} 

Electric  Figures,  Lichtenberg's.— (See  Figures,  Elec- 
tric, Lichtenberg's.) 

Electric  Fishes.— (See  Fishes,  Electric.} 
Electric  Flyer,  or  Fly.— (See  Flyer,  Electric.} 
Electric  Fog.— (See  Fog,  Electric.} 

Electric  Force.— The  force  developed  by  electricity. 
This  term  is  generally  limited  to  the  force  of  attraction  or 
repulsion  produced  by  an  electrostatic  charge. 

Electric  Furnace.— (See  Furnace,  Electric.} 
Electric  Fuse.— (See  Fuse,  Electric.} 
Electric  Gas  Lighting.— (See  Gas  Lighting,  Electric.) 
Electric  Gilding.— (See  Gilding,  Electric.) 


WORDS,  TERMS  AND  PHRASES.  210 

Electric  Governor. — (See  Governor,  Electric.) 

Electric  Head  Light.— (See  Head  Light,  Electric.) 

Electric  Heat. — (See  Heat,  Electric.) 

Electric  Heater.— (See  Heater,  Electric.) 

Electric  Horse  Power. — (See  Horse  Power,  Electric.) 

Electric  Hydrotasimeter.— (See  Hydrotasimeter,  Elec- 
tric.) 

Electric  Ignition.— (See  Ignition,  Electric.) 
Electric  Images.— (See  Images,  Electric.) 
Electric  Incandescence.— (See  Incandescence,    Elec- 
tric.) 

Electric  Indicators.— (See  Indicators,  Electric.) 
Electric  Insolation.— (See  Sunstroke,  Electric.) 
Electric  Jewelry. — (See  Jewelry,  Electric.) 
Electric  Lamp,  Arc. — (See  Lamp,  Electric,  Arc.) 
Electric  Lamp,  Incandescent. — (See  Lamp,  Incan- 
descent.) 

Electric  Lamp,    Semi-Incandescent.— (See   Lamp, 
Semi-Incandescent.) 

Electric  Letter-Box.— (See  Letter-Box,  Electric.) 
Electric  Locomotive.— (See  Locomotive,  Electric.) 
Electric  Log.— (See  Log,  Electric.) 
Electric  Loop.— (See  Loop,  Electric.) 

Electric  Machines,  Electrostatic  Induction 

— (See  Machines,  Electrostatic  Induction.) 

Electric  Machines,  Frictional (See     achin 

Electric,  Frictional.) 

Electric  Mains.— (See  Mains,  Electric.) 
Electric  Masses.— (See  Masses,  Electric.) 
Electric  Measurement.— (See  Measurement,  Electric.) 


2&0  A  DICTIONARY  OF  ELECTRICAL 

Electric  Meter.— (See  Meter,  Electric.") 
Electric  Mine  Exploder.— (See  Fuse,  Electric.) 
Electric  Motor. — (See  Motor,  Electric.) 
Electric  Musket.— (See  MusJcet,  Electric.) 
Electric  Organ.— (See  Organ,  Electric.) 
Electric  Oscillations. — (See  Oscillations,  Electric.) 
Electric  Osmose.— (See  Osmose,  Electric.) 
Electric  Pen.— (See  Pen,  Electric.) 
Electric  Pendulum.— (See  Pendulum,  Electric.) 
Electric    Phosphorescence.  —  (See  Phosphorescence, 
Electric.) 

Electric  Piano.— (See  Piano,  Electric.) 
Electric  Plough. — (See  Plough,  Electric.) 
Electric  Potential.— (See  Potential,  Electric.) 
Electric  Probe.— (See  Probe,  Electric.) 
Electric  Prostration.— (See  Sunstroke,  Electric.) 
Electric  Protection. — (See  Lightning  Rods.) 

Electric  Protection  of  Metals.— (See  Metals,  Elec- 
tric Protection.) 

Electric  Pyrometer.— (See  Pyrometer,  Electric.) 

Electric  Ray  (Raia  torpedo). — A  species  of  fish  named 
the  ray,  which,  like  the  electric  eel,  possesses  the  power  of 
producing  electricity. 

The  electric  organ  is  situated  at  the  back  of  the  head,  and 
consists  of  hundreds  of  polygonal,  cellular  laminae,  supplied 
with  numerous  nerve  fibres,  as  shown  in  Fig.  167. 

Electric  Rectification  of  Alcohol.— (See  Alcohol, 
Electric  Rectification  of.) 

Electric  Register,  Watchman's (See  Watch- 
man's Electric  Register.) 


WORDS,  TERMS  AND  PHRTASES. 


221 


Electric  Registering  Apparatus.— (Se 

Apparatus,  Electric. ) 

Electric  Resistance.— (See  Resistance,  Electric.) 
Electric  Safety  Lamp.— (See  Safety  Lamp,  Electric.) 
Electric  Seismograph.— (See  Seismograph,  Electric.) 

Electric    Shadow.— (See 

Shadow,  Electric.) 

Electric  Shock.— (See  Shock, 
Electric.) 

Electric  Socket  for  Lamp. 

—(See  Socket,  Electric  Lamp.) 

Electric  Soldering.— (See  Sol- 
dering, Electric.) 

Electric  Storms.— (See  Storms, 
Electric.) 

Electric  Striae.— (See  S trice, 
Electric.) 

Electric  Sunstroke.  — (See 
Sunstroke,  Electric.) 

Electric  Target.— (See  Target, 
Electric.) 

Electric  Teazer.— (See  Teaz- 
er,  Electric  Current.) 

Electric  Tempering.— A  pro- 
cess for  tempering  metals  in  which 
heat  of  electric  origin  is  employed  fig.  167. 

instead  of  ordinary  furnace  heat.     (See  Tempering,  Electric.) 
Electric  Tension.— (See  Tension,  Electric.) 
Electric  Thermometer.— (See  Thermometer,  Electric.) 
Electric  Time-Ball.— (See  Time-Ball,  Electric.) 
Electric  Torpedo,— (See  Torpedo,  Electric.) 


222  A  DICTIONARY  OF  ELECTRICAL 

Electric  Tower. — (See  Tower,  Electric) 
Electric  Transmitters.— (See  Transmitters,  Electric.} 
Electric  Typewriter.— (Sec  Typewriter,  Electric.} 
Electric  Valve.— (See  Valve,  Electric.} 
Electric  Varnish.— (See  Varnish,  Electric.) 
Electric  Welding.— (See  Welding,  Electric.} 
Electric  Whirl.— (See  Whirl,  Electric.) 
Electric  Whistle.— (See  Whistle,  Steam,  Electric.) 
Electric  Work.— (See  Work,  Electric.) 
Electrical  Convection  of  Heat.— A  term  employed 
to  express  the  dissymmetrical   distribution   of  temperature 
that   occurs  when  a  current  of  electricity  is  sent  through  a 
metallic  wire,  the  middle  of  which  is  maintained  at  a  con- 
stant temperature,  and  the  ends  at  the  temperature  of  melt- 
ing ice. 

Electrical  Death.— (See  Death,  Electrical) 
Electricity.— The  name  given  to  the  unknown  thing, 
matter, or  force,  or  both,  which    is  the  cause  of  electric  phe- 
nomenon. 

Electricity,  no  matter  how  produced,  is  believed  to  be  one 
and  the  same  thing. 

The  terms  frictional  electricity,  pyro-electricity,  magneto 
electricity,  voltaic  or  galvanic  electricity,  thermo-electricity, 
contact  electricity,  animal  or  vegetable  electricity,  etc.,  etc., 
though  convenient  for  distinguishing  their  origin,  have  no 
longer  the  significance  formerly  attributed  to  them  as  repre- 
senting different  kinds  of  the  electric  force.  (See  Electricity, 
Hypotheses  of.) 

Electricity,  Conservation  of A  term  proposed 

by  Lippman,  to  express  the  fact  that  when  a  body  receives  an 
electric  charge  in  the  open  air,  the  earth  and  heavenly 
bodies  receive  an  equal  and  opposite  charge,  thus  preserving 


WORDS,  TERMS  AND  PHRASES.  223 

the  sum  of  the  total  positive  and  negative  electricities  in  the 
universe. 
Electricity,    Double    Fluid     Hypothesis    of.— A 

hypothesis  which  endeavors  to  explain  the  cause  of  electric 
phenomena  by  the  assumption  of  two  different  electric  fluids. 
The  Double  Fluid  Electric  Hypothesis  assumes  : 

(1)  That  the  phenomena  of  electricity  are  due  to  two  ten- 
uous and  imponderable  fluids,   the  positive  and  the  nega- 
tive. 

(2)  That  the  particles  of  the  positive  fluid  repel  one  another, 
as  do  also  the  particles  of  the  negative  fluid  ;   but  that  the 
particles  of  positive  fluid  attract  the  particles  of  the  negative, 
and  vice  versa. 

(3)  That  the  two  fluids  are  strongly  attracted  by    matter, 
and  when  present  in  it  produce  electrification. 

(4)  That  the  two  fluids  attract  one  another  and  unite,  thus 
masking  the  properties  of  each. 

(5)  That  the  act  of  friction  separates  these  fluids,  one  going 
to  the  rubber  and  the  other  to  the  thing  rubbed. 

Electricity,  Single  Fluid  Hypothesis  of.— A 
hypothesis  which  endeavors  to  explain  the  cause  of  electrical 
phenomena  by  the  assumption  of  a  single  electric  fluid. 

The  single-fluid  hypothesis  assumes  : 

(1)  That  the  phenomena  of  electricity  are  due  to  the  pres- 
ence of  a  single,  tenuous,  imponderable  fluid. 

(2)  That  the  particles  of   this  fluid    mutually  repel    one 
another,  but  are  attracted  by  all  matter. 

(3)  That  every  substance  possesses  a  definite  capacity  for 
holding  this  fluid,  and,  that  when  this  capacity  is  just  satisfied 
no  effects  of  electrification  are  manifest. 

(4)  That  when  the  body  has  less  than  this  quantity  present, 
it  becomes  negatively  excited,  and  when  it  has  more,  positively 
excited. 

(5)  That  the  act  of  friction  causes  a  redistribution  of  the 
fluid,  part  of  it  going  to  one  of  the  bodies,  giving  it  a  surplus, 


224  A  DICTIONARY  OF  ELECTRICAL 

and  thus  positively  electrifying  it,  and  leaving  the  other  with 
a  deficit,  and  thus  negatively  electrifying  it. 

Neither  of  these  hypotheses  is  accepted  at  the  present 
time,  electrical  science  having  advanced  sufficiently  far  to  rec- 
ognize the  fact  that  the  exact  nature  of  electricity  is  unknown. 

By  some,  electricity  is  believed  to  consist,  like  heat,  of  a  par- 
ticular phase  of  energy  ;  by  others  it  is  regarded  as  an  exceed- 
ingly tenuous  form  of  matter ;  by  still  others,  the  exceedingly 
strange  assumption  is  made  that  it  is  neither  a  phase  of  energy 
nor  a  form  of  matter. 

By  some,  the^  single  fluid  hypothesis  is  provisionally  ac- 
cepted with  this  modification,  that  a  negatively  excited  body 
is  thought  to  be  the  one  which  contains  the  excess  of  the  as- 
sumed fluid,  and  a  positively  excited  body  the  one  which 
contains  the  deficit. 

This  change  in  the  single  fluid  hypothesis  is  believed  to  be 
necessitated  by  the  fact  observed  in  Crooke's  tubes,  that  the 
molecules  of  residual  gas  are  thrown  off  from  the  negative 
terminal,  and  not  from  the  positive  terminal.  (See  Tubes, 
CrooMs.) 

Another  view,  which  has  long  been  held  by  the  author,  at- 
tributes the  phenomena  of  electricity  to  differences  of  ether 
pressures,  electricity  itself  being  the  ether,  and  the  electro- 
motive force  the  differences  of  pressure  of  the  ether.  That 
one  form  of  electrification,  possibly  negative,  is  caused  by  a 
surplusage  of  energy  charged  on  the  excited  body,  thus 
producing  a  greater  ether  tension  or  pressure,  and  the  oppo- 
site electrification,  by  a  deficit  of  energy,  thus  producing  a 
smaller  ether  tension  or  pressure. 

It  will  be  seen  that  the  assumptions  as  to  the  direction  of  the 
current,  and  the  positive  direction  of  the  lines  of  force,  are 
based  on  the  old  idea  that  positive  electrification  indicates  an 
excess,  and  negative  electrification  a  deficit. 

Electricity,  Bound  and  Free,  Disguised,  Dissimu- 
lated, or  Latent (See  Bound  and  Free  Charge.) 


WORDS,  TERMS  AND  PHRASES.  225 

Electrics. — Substances  capable  of  becoming  electrified  by 
friction. 

Substances  like  the  metals,  which,  when  held  in  the  hand 
could  not  be  electrified  by  friction  were  called  non-electrics. 

These  terms  were  used  by  Gilbert  in  the  early  history  of 
the  science. 

This  distinction  is  not  now  generally  employed,  since  con- 
ducting substances  may  be  electrified  by  friction,  if  insulated. 

Electrification.— The  act  of  becoming  electrified. 

Electrification  generally  refers  to  the  production  of  an  elec- 
tric charge. 

Electro-Biology.— The  study  of  the  electric  conditions 
of  living  animals  and  plants,  or  the  effects  of  electricity  upon 
them. 

Electro-Biology  includes  : 

(1)  Electro-Physiology. 

(2)  Electro-Therapy,  or  Electro-Therapeutics. 
Electro-Capillary    Phenomena.  —  Phenomena    ob- 
served in  capillary  tubes  at  the  contact  surfaces  of  two  liquids. 

In  the  case  where  acidulated  water  is  in  contact  with 
mercury,  each  liquid  possesses  a  definite  surface  tension,  and 
each  a  definite  shape  of  surface. 

The  two  liquids,  however,  do  not  actually  touch,  there  being 
a  small  interval  or  space  between  them.  This  space  acts  as 
an  accumulator.  But  the  liquid  and  water,  being  different 
substances  in  contact,  possess  different  potentials.  (See  Ac- 
cumulator, or  Condenser.  Contact,  Electricity.  Potential.) 

Any  cause  which  alters  the  shape  of  these  contact  surfaces, 
and  consequently  the  extent  of  the  spaces  between  them, 
necessarily  alters  the  capacity  of  the  condenser,  and  conse- 
quently the  difference  of  potential.  Therefore  the  mere 
shaking  of  the  tube,  or  heating  it,  will  produce  electric 
currents  from  the  resulting  differences  of  potential ;  or,  con- 
versely, an  electric  current  sent  across  the  contact-surfaces 
will  produce  motion  as  a  result  of  a  change  in  the  value  of 


226  A  DICTIONARY   OF  ELECTRICAL 

the  surface  tension.  An  Electro-  Capillary  Telephone  has  been 
constructed  on  the  former  principle,  and  an  Electrometer  on 
the  latter.  (See  Capillary  Electrometer.  Telephone,  Electro- 
Capillary.) 

Electro-Chemistry.— That  branch  of  electric  science 
which  treats  of  chemical  compositions  and  decompositions 
produced  by  the  electric  current.  (See  Electrolysis,  or  Elec- 
trolytic Decomposition.) 

Electrode,  Indifferent In  electro-thera- 
peutics the  electrode  that  is  merely  employed  to  complete  the 
circuit  through  the  organ  or  part  subjected  to  the  electric 
current,  and  is  not  directly  concerned  in  the  treatment  or 
diagnosis  of  the  diseased  parts. 

Either  the  positive  or  the  negative  electrode  may  be  the 
indifferent  electrode.  (See  Electrode,  Therapeutic.) 

Electrode,  Therapeutic In  electro-ther- 
apeutics the  electrode  mainly  concerned  in  the  treatment,  or 
diagnosis  of  the  diseased  parts. 

Either  the  positive  or  the  negative  electrode  may  be  the 
therapeutic  electrode,  and  one  or  the  other  is  employed  accord- 
ing to  the  particular  character  of  the  effect  it  is  desired  to  ob- 
tain. The  other  electrode  is  placed  at  any  convenient  and 
suitable  part  of  the  body,  and  is  called  the  indifferent 
electrode. 

The  therapeutic  electrode  is  generally  placed  nearer  the 
organ  or  part  to  be  treated  than  the  indifferent  electrode. 

Electrodes.— The  terminals  of  an  electric  source. 

The  positive  electrode  is  sometimes  called  the  Anode,  and 
the  negative  electrode  the  Kathode.  In  precise  use  these 
terms  are  generally  restricted  to  the  electrodes  when  used 
for  electrolytic  decomposition. 

The  electrodes  are  made  of  different  shapes  and  of  different 
materials  according  to  the  Character  of  the  work  the  current 
is  to  perform. 


WORDS,  TERMS  AND  PHRASES.  227 

The  carbon  electrodes  of  an  arc  lamp  are  provided  for  the 
formation  and  maintenance  of  the  voltaic  arc.  In  electro-ther- 
apeutics, clay  electrodes,  sponge  electrodes,  brush  electrodes, 
disc  electrodes,  needle  electrodes,  dry  or  moist  electrodes, 
urethral  electrodes,  aural  electrodes,  vaginal  electrodes,  rectal 
electrodes,  etc.,  etc.,  are  employed,  and  are  named  according 
to  the  nature  of  the  work  required  to  be  accomplished,  or  the 
particular  organ  or  part  of  the  body  that  is  to  be  treated. 

Electrodes,  Erb's  Standard  Size  of Standard 

sizes  of  electrodes  generally  adopted  in  electro-therapeutics. 

The  following  standard  sizes  have  been  proposed  by  Erb, 
viz.: 

(1)  Fine  electrode %  centimetre  diameter. 

(2)  Small       "        2  "  " 

(3)  Medium   "       ..7.5  "  " 

(4)  Large       "       6x2        "  " 

(5)  Very  large  do ...8  x  16     " 

Electro-Diagnosis.— Diagnosis  by  means  of  the  exagger- 
ation or  diminution  of  the  reaction  of  the  excitable  tissues  of 
the  body  when  subjected  to  the  varying  influences  of  electric 
currents. 

The  electric  current  has  also  been  applied  in  order  to  dis^ 
tinguish  between  forms  of  paralysis,  and  as  a  final  test  of 
death. 

Electro-Dynamic  Induction.— (See  Induction,  Elec- 
tro-Dynamic.} 

Electro-Dynamics. — That  branch  of  electric  science 
which  treats  of  the  action  of  electric  currents  on  one  another 
and  on  themselves. 

The  principles  of  electro-dynamics  were  discovered  by  Am- 
pere in  1821. 

A  convenient  form  of  apparatus,  for  showing  experimentally 
the  action  of  one  current  on  another,  consists  of  two  upright 
metallic  columns  or  pillars,  which  support  horizontal  metallic 
arms  containing  mercury  cups,  y  and  c,  Fig.  168.  The  circuit 


228  A  DICTIONARY  OF   ELECTRICAL 

is  beat  in  the  form  of  a  rectangle,  circle,  or  solenoid,  and  ter- 
minates in  points  that  dip  in  the  mercury  cups.  The  current 
is  led  into  and  out  of  the  apparatus  at  the  points  -f  and  — 
at  the  base  of  the  upright  supports. 

When,  now,  a  magnet,  or  another  circuit,  is  approached  to 
the  movable  circuit  thus  provided,  attractions  or  repulsions 
are  produced  according  to  the  position  of  the  magnet,  or  the 
direction  of  the  currents  in  the  two  circuits. 


B  B 


Fig.  168. 

It  a  magnet  A  B,  Fig.  169,  be  placed,  as  shown,  below  the 
movable  circuit  C  C,  the  circuit  will  tend  to  place  itself  at 
right  angles  to  the  axis  of  the  magnet.  This  movement  is  the 
same  as  would  occur  if  electric  currents  were  circulating 
around  the  magnet  in  the  direction  of  the  assumed  Ampdrian 
currents.  (See  Magnetism,  Ampere's  Theory  of.) 


\VORDS,  TERMS  AND  PHRASES. 


Ampere  has  given  the  results  of  his  investigations  in  the 
following  statements,  which  are  known  as  Ampere's  Laws : 

(1)  Parallel  portions  of  a  circuit  attract  one  another  if  the 
currents  in  them  are  flowing 

in  the  same  direction,  and 
repel  one  another  if  the  cur- 
rents are  flowing  in  opposite 
directions. 

A  current  flowing  through 
a  spiral  tends  to  shorten  the 
spiral  from  the  attraction  of 
the  parallel  currents  in  con- 
tiguous turns. 

Similar  poles  of  two  sole- 
noids repel  each  other,  as  at 
A,  A',  Fig.  170,  because, 
when  opposed  to  each  other, 
the  currents  that  produce 
these  poles  are  flowing  in  opposite  directions,  as  may  be  seen 
from  an  inspection  of  the  drawing. 

Dissimilar  solenoid  poles,  on  the  contrary,  attract  each  other 
as  at  A,  B,  in  the  figure,  since  the  currents  which  produce 
them  flow  in  the  same  di- 
rection. 

In  Fig.  171,  a  form  of  Am- 
pere's stand  is  shown,  in 
which  one  of  the  circuits  is 
in  the  form  of  the  helix  M 
N ;  its  action  on  the  movable 
circuit  C  B,  is  to  repel  it, 
.A  &  since  the  currents,  as  shown, 

Fiff-  17°-  are  flowing  in  opposite  di- 

rections in  the  approached  portions  of  the  fixed  and  movable 
circuits. 

(2)  Two  portions  of  a  circuit  intersecting  each  other  mu- 


Fiff. 


236  A  DICTiO-tf ART  OF  ELECTRICAL 

tually  attract  each  other  when  the  currents  in  both  circuits 
flow  either  towards  or  from  the  point  of  intersection,  but  re- 
pel each  other  if  they  flow  in  opposite  directions  from  the 
point 

Thus,  in  Fig.  172,  the  currents  in  both  circuits  flow  towards 
and  from  the  point  of  intersection  Y,  and  attract  one  another 
and  cause  a  motion  until  the  two  circuits  are  parallel 


Fig.  in. 

If  the  currents  flow  in  opposite  directions  they  repel  one 
another,  and,  if  free  to  move,  will  come  to  rest  when  parallel 
to  each  other ;  therefore,  two  portions  of  a  circuit  crossing 
each  other  tend  to  move  until  they  are  pai-allel,  and  their  cur- 
rents are  flowing  in  the  same  direction. 

(3)  Successive  portions  of  the  circuit  of  the  same  rectilineal 
current,  that  is,  a  current  flowing  in  the  same  straight  line,  re- 
pel one  another. 

Continuous  Rotations  by  Currents. — A  circuit  O  A,  Fig.  173, 
movable  on  O,  as  a  centre,  will  be  continuously  rotated  in  the 
direction  of  the  curved  arrow  by  the  rectilinear  current,  P  Q ; 


WORDS,  TERMS  AND  PHRASES. 


for,  the  directions  of  the  currents  being  as  shown  by  the  ar- 
rows, there  will  be  attraction  in  the  positions  (1)  and  (2),  and 
repulsion  in  position  (4). 

The  cause  of  the  mutual  attractions  and  repulsions  of  elec- 
tric circuits  will    readily   appeal* 
from  a  consideration  of  the  mutual 
action  of  their  magnetic  fields. 

Thus  an  inspection  of  Fig.  174, 
shows : 

(1)  That  parallel  currents  flow- 
ing in  the  same  direction  attract, 
because  their  lines  of  force  have 
opposite  directions  in  adjoining 
parts  of  the  circuit. 

(2)  That  parallel  currents  flow-  g_J. 
ing  in  opposite  directions  repel, 
because  their  lines  of  force  have 

the  same  direction  in  adjoining 

parts  of  the  circuit.  fig-  m. 

These  laws  may  therefore  be  generalized  thus,  viz. :  Lines 
of  force  extending  in  opposite  directions  attract  one  another; 
lines  of  force  extending  in  the  same 
direction  repel  one  another. 

Ampere  proved  that  a  circuit,  doubled 
on  itself  so  that  the  current  flows  in 
opposite  directions  in  the  two  parts, 
exerts  no  force  on  external  objects. 
This  expedient  is  adopted  in  resistance 
p  Q  coils  to  prevent  any  disturbance  of  the 

Fig.  173.  galvanometer  needles.    He  also  showed 

that  a  sinuous  circuit,  or  one  bent  into  zigzags,  produces  the 
same  effects  of  attraction  or  repulsion  as  it  would  if  it  were 
straight.  (See  Coils,  Resistance.) 

The  term  sinuous  current  is  often  applied  to  the  current  in 
such  a  conductor.     (See  Currents,  Sinuous.) 


\ 


232 


A  DICTIONARY  OF  ELECTRICAL 


Electro-Dynamometer.  —  (See  Dynamometer,  Electric.} 

Electro-Etching.—  (See  Engraving,  Electric). 

Electrokinetics.  —  A  term  sometimes  applied  to  the  phe- 
nomena of  electric  currents,  or  electricity  in  motion,  as  dis- 
tinguished from  Electrostatics,  the  phenomena  of  electric 
charges,  or  electricity  at  rest. 

Electrolier.—  A  chandelier  for  electric  lights,  as  dis- 
tinguished from  a  chandelier  for  holding  gas  lights. 

Electrolysis,  Faraday's  Lairs  of  --  The  pi-in- 
cipal  facts  of  electrolysis  are  given  in  the  following  laws  : 

(1)  The  amount  of  chemical  action  in  any  given  time  is  equal 
in  all  parts  of  the  circuit. 


Fig.  17U. 

(2)  The  amount  of  any  ion  liberated  in  a  given  time,  is  pro- 
portional to  the  strength  of  the  current  passing.     Twice  as 
great  a  current  will  liberate  twice  as  much  of  an  ion. 

(3)  When  the  same  current   passes   successively  through 
several  cells  containing  different  electrolytes,  the  weights  of  the 
ions  liberated  at  the  different  electrodes  are  equal  to  the 
strength  of  the  current  multiplied  by  the  electro-chemical 
equivalent  of  the  ion. 

The  electro-chemical  equivalent  is  equal  to  tlie  atomic  u'eight 
divided  by  the  valency.    (See  Equivalent,  Electro-  Chemical. ) 


WORDS,  TERMS  AND  PHRASES.  233 

Electrolysis,  or   Electrolytic    Decomposition.— 

Chemical  decompositions  effected  by  means  of  the  electric 
current. 

When  an  electric  current  is  sent  through  an  electrolyte,  i.  e., 
a  liquid  which  permits  the  current  to  pass  only  by  means  of  the 
decomposition  of  the  liquid,  the  decomposition  that  ensues 
is  called  electrolytic  decomposition. 

The  electrolyte  is  decomposed  or  broken  up  into  atoms  or 
groups  of  atoms  or  radicals,  called  ions. 

The  ions  are  of  two  distinct  kinds,  viz. :  the  electro-positive 
ions,  or  kathions  or  kations,  and  the  electro-negative  ions 
or  anions. 

Since  the  anode  of  the  source  is  connected  with  the  electro- 
positive terminal,  it  is  clear  that  the  anions,  or  the  electro- 
negative ions,  must  appear  at  the  anode,  and  the  kathions,  or 
the  electro-positive  ions,  must  appear  at  the  kathode. 

Hydrogen,  and  the  metals  generally,  are  kathions  ;  oxygen, 
chlorine,  iodine,  etc.,  are  anions. 

The  vessel  containing  the  electrolyte,  in  which  these  de- 
compositions take  place,  is  called  an  electrolytic  cell. 

An  electrolytic  cell  is  called  a  voltameter,  when  it  is 
arranged  for  measuring  the  current  passing  by  means  of 
the  amount  of  decomposition  it  effects.  (See  Voltameters.) 

Electrolytic  Convection.— (See  Convection,  Electro- 
lytic.) 

Electro-Magnet. — A  magnet  produced  by  the  passage  of 
an  electric  current  through  a  coil  of  insulated  wire  surround- 
ing a  core  of  magnetizable  material. 

The  magnetizing  coil  is  called  a  helix  or  solenoid.  (See  Mag- 
netism, Ampere's  Theory  of.  Solenoid,  Electro-Magnetic.) 

Strictly  speaking,  the  term  electro-magnet  is  limited  to  the 
case  of  a  magnet  pro%rided  with  a  soft  iron  core,  which  is  thus 
enabled  to  rapidly  acquire  its  magnetism  on  the  passage  of  the 
magnetizing  current,  and  as  readily  to  lose  its  magnetism  on 
the  cessation  of  such  cuiTent. 


234  A  DICTIONARY  OF  ELECTRICAL 

An  electric  current  passed  around  a  bar  of  magnetizable 
material,  in  the  manner  and  direction  shown  in  Fig.  175,  will 
produce  a  polarity  at  its  ends  or  extremities. 

The  direction  of  this  polarity  may  be  predicted  by  the  fol- 
lowing modifications  of  a  rule  proposed  by  Ampere  : 


Fig.  175. 

Imagine  yourself  swimming  in  the  wire  in  the  direction  of 
the  current;  if,  then  your  face  is  directed  towards  the  bar 
that  is  being  magnetized,  its  north  seeking  pole  will  be  on 
your  left. 

If,  for  example,  the  conductor  A  B  be  traversed  by  a  cur- 
rent in  the  direction  from  B  to  A,  as  shown  in  Fig.  177, 
the  north  pole  N,  of  the  needle  N  S,  placed  under  the  con- 
ductor, is  deflected,  as  shown,  to  the  left  of  the  observer,  who 
is  supposed  to  be  swimming  in  the  current,  facing  the  needle. 
If  the  current  flow  in  the  opposite  direction,  as  from  A  to  B,  as 
shown  in  the  Fig.  178,  the  N  pole  of  the  needle  is  deflected  as 
shown,  but  still  to  the  left  of  the  observer  supposed  to  be  swim- 
ming as  before. 

The  directions  of  currents  required  to  produce  N  and  S  poles 
respectively,  are  shown  in  Fig.  176. 

The  cause  of  this  direction  of  polarity  will  be  readily  un- 
derstood from  a  study  of  the  direction  of  lines  of  magnetic 
force  in  the  field  produced  by  an  electric  current. 


WORDS,  TERMS  AND  PHRASES. 


S35 


In  any  electric  circuit,  the  lines  of  magnetic  force,  produced 
by  the  passage  of  the  current, 
form  circles  around  the  circuit 
in  planes  at  right  angles  to 
the  direction  of  the  current, 
as  shown  in  Fig.  179.  The 
direction  of  these  lines  of 
force  is  the  same  as  that  of 
the  hands  of  a  watch,  if  the  Fig-  m- 

current  be  supposed  to  flow  away  from  the  observer.    (See 
Field,  Magnetic,  of  an  Electric  Current.) 


Fig.  178.  Fig.  177. 

Remembering  now  that  the  lines  of  force  are  supposed  to 
come  out  of  the  north  pole  and  to  pass  into  the  south  pole, 
it  is  evident  that  if  the  current  flows  in  the  direction  shown  in 
Fig.  180,  the  lines  of  force  will  come  out  of  the  north  pole 
and  pass  into  the  south  pole. 


A  DICTIONARY  OF  ELECT RICAL 


Since  in  a  right  handed  helix  the  wire  passes  around  the 
axis  in  the  opposite  direction  to  that  in  which  it  passes  in  a  left 
handed  helix,  it  is  evident  that  the  helices  shown  in  Fig.  181 

at  1   and  2,    will 
produce  opposite 

p°lafie*  at  the 

points  of  entrance 
and  exit  by  a  cur- 
rent flowing  in  the 
direction  of  the  ar- 
Flg.  179.  rows. 

If  the  current  be  sent  through  the  right  handed  helix,  shown 
at  1,  from  b  to  a,  that  is,  from  the  left  to  the  right  in  the  figure, 
a  soutli  pole  will  be  produced  at  &,  and  a  north  pole  at  a. 
If,  however,  it  be  sent  from  a  to  &,  the  polarity  will  be  re- 
versed. 


Fig.  180. 

If  the  current  be  sent  through  the  left  handed  helix,  shown 
at  2,  from  a,  to  6,  that  is,  from  the  left  to  the  right  in  the  figure, 
a  north  pole  will  be  produced  at  a,  and  a  south  pole  at  6.  If, 


WORDS,  TERMS  AND  PHRASES. 


237 


however,  it  be  sent  in  the  opposite  direction  the  polarity  will 
be  reversed. 

Therefore,  in  an  electro  magnet,  on  the  core  of  which 
several  layers  or  thicknesses  of  wire  are  wound,  in  which 
the  current  flows  through  one  layer,  in,  say  a  direction  from 
right  to  left,  it  must  return  through  the  next  layer  in  the 
opposite  direction,  or  from  left  to  right.  The  polarities  of  the 
same  extremities  of  the  helices  are,  however,  the  same  in  all 
cases,  since  the  layers  are  successively  right  and  left  handed. 
The  winding  at  3  produces  a  number  of  consequent  poles. 

Electro-Magnets,  Laws  of. 


3  a 


Fig,  181. 


(1)  The  magnetic  intensity  (strength)  of  an  electro  magnet 
is  nearly  proportional   to  the   strength  of  the  magnetizing 
current,  provided  the  core  is  not  saturated. 

(2)  The  magnetic  strength  is  proportional  to  number  of  turns 
of  wire  in  the  magnetizing  coil. 

(3)  The  magnetic  strength  is  independent  of  the  thickness  or 
material  of  the  conducting  wires. 

These  laws  may  be  embraced  in  the  more  general  statement 
that  the  strength  of  an  electro  magnet,  the  size  of  the  magnet 
being  the  same,  is  'proportional  to  the  number  of  its  Ampere 
Turns.  (See  Ampere-Turns.} 


238  A  DICTIONARY   OF  ELECTRICAL 

A  short  interval  of  time  is  required  for  a  current  to 
thoroughly  magnetize  a  powerful  electro-magnet. 

A  few  moments  are  also  required  for  a  powerful  magnet  to 
thoroughly  lose  its  magnetism.  At  the  same  time,  electro 
magnets  are  capable  of  acquiring  or  losing  their  magnetism 
several  thousand  times  a  second.  It  is,  In  fact,  on  this  ability 
possessed  to  so  remarkable  a  degree  by  soft  iron,  that  the  value 
of  an  electro  magnet  for  many  purposes  depends.  (See  Lag, 
Magnetic.) 

Electro-Magnetic  Annunciator.— (See  Annunciator, 
Electro-Magnetfc.) 

Electro-Magnetic  Dental  Mallet. — (See  Dental  Mal- 
let, Electro-Magnetic.) 

Electro-Magnetic  Drill.— (See  Drill,  Electro- Magnetic.) 

Electro-Magnetic  Engine.— (See  Engine,  Electro-Mag- 
netic.) 

Electro-Magnetic  Induction.— A  variety  of  electro- 
dynamic  induction  in  which  electric  currents  are  produced  by 
the  motion  of  electro  magnets,  or  electro-magnetic  solenoids. 
(See  Induction,  Electro-Dynamic.) 

Electro-Magnetic  Solenoid.— (See  Solenoid,  Electro- 
Magnetic.) 

Electro-Magnetic  Stress The  force  or  pres- 
sure in  a  magnetic  field  which  produces  a  strain  or  deformation 
in  a  piece  of  glass  or  other  similar  svibstance  placed  therein. 
(See  Optical  Strain,  Electro-Magnetic.) 

Electro-Magnetics. — That  branch  of  electric  science 
which  treats  of  the  relations  between  electric  currents  and 
magnets. 

Electro-Metallurgy.— Metallurgical  processes  effected 
by  the  agency  of  electricity. 

Electro-Metallurgy  embraces  : 

(1)  The  Reduction  of  Metals  from  their  ores,  either  directly 
from  their  fusion  by  the  heat  ol  the  voltaic  arc,  or  the  heat  of 


WORDS,  TERMS  AM>  PHRASES 


239 


incandescence,  or  by  the  electrolysis  of  solutions  of  their  ores, 
(See  Electrolysis.    Furnace,  Electric.) 

(2)  Electroplating. 

(3)  Electrotyping. 

The  application  of  electricity  to  the  reduction  of  metals  is 
carried  on  in  the  electric  furnace  for  the  reduction  of  the 
aluminium  ores. 

Electrometer. — An  apparatus  for  measuring1  differences 
of  potential. 

Electrometers,  operate  in  general,  by  means  of  the  attraction 
or  repulsion  of  charged  conductors  on  a  suitably  suspended 
needle  or  disc.  As  no  current  is  required  to  flow  through  the 
apparatus  it  is  adaptable  to  many  cases  where  a  voltmeter 
could  not  be  so  readily  used. 

Electrometer,  Absolute A  form  of  attracted 

disc  electrometer.    (See  Electrometer,  Attracted  Disc.) 

Electrometer,  Attracted  Di§c A   form   of 

electrometer  de- 
vised by  Sir  Wm. 
Thomson,  in 
which  the  force 
is  measured  by 
the  attraction  be- 
tween two  discs. 

Thomson's  At- 
tracted Disc  Elec- 
trometer  is 
shown  in  Fig.  182. 
It  consists  of  a 
plate  C,  suspend- 
ed from  the  longer  end  of  a  lever  I,  within  the  fixed  guard 
plate,  or  guard  ring,  B,  immediately  above  a  second  plate 
A,  supported  on  an  insulated  stand,  and  capable  of  a  meas- 
urable approach  towards  C,  or  a  movement  away  from  it. 
The  plate  C,  is  placed  in  contact  with  B,  by  means  of  a  thin 


Fig.  182. 


A  DICTIONARY  OF  ELECTRICAL 


Fig.  183. 


wire.  By  means  of  this  connection  the  distribution  of  the 
charge  over  the  plate  C,  is  uniform.  The  electrostatic  at- 
traction is  measured  by  the  attrac- 
tion of  the  fixed  disc  A,  or  the 
movable  disc  C.  The  fulcrum  of 
the  lever  Z,  is  formed  of  an  alu- 
minium wire,  the  torsion  of  which 
is  used  to  measure  the  force  of  the 
attraction,  or,  it  may  be  meas- 
ured directly  by  the  counterpoise 
weight  Q. 

This  instrument  is  called  an  ab- 
solute electrometer,  because,  knowing  the  dimensions  of  the 
apparatus,  the  value  of  the  electro-motive  force  can  be  directly 
determined  from  the  amount 
of  the  motion  observed. 

Electrometer,  Capil- 
lary  (SeeCapillary 

Electrometer.) 

Electrometer,  Quad- 
rant    — An  electro- 
meter in  which  the  electro- 
static charge  is  measured  by 
the  attractive  force  of  plates 
or  quadrants,  a,  &,  c,  d,  Fig. 
183,  on  a  light  needle  u,  of 
aluminium  suspended  within 
them. 

The  sectors  or  quadrants 
are  of  brass,  and  are  so 
shaped  as  to  form  a  hollow 
cylindrical  box  when  placed 
together.  The  four  sectors 


Fig.  286. 


or  quadrants,  are   insulated  from  one  another,  but  the   op- 
posite ones  are  connected  by  a  conducting  wire,  as  shown 


WORDS,  TERMS  AND  PHRASES. 


241 


in  Fig.  183.  A  light  needle  of  aluminium  that  is  main- 
tained at  some  constant  potential,  by  connection  with  the 
inner  coating  of  a  Leyden  jar,  is  generally  suspended  by  two 
parallel  silk  threads,  so  that  it  freely  swings  inside  the  hollow 
box,  and,  when  at  rest,  is  in  the  position,  as  shown  by  the 
dotted  lines,  with  its  axis  of  symmetry  exactly  under  one  of 

the  slots  or  spaces  be- 
tween the  opposite  sec- 
tors. (See  Bi-Filar  Sus- 
pension.) 

The  quadrant  electro- 
meter is  shown  in  Fig. 

184,  with    one    of    the 
quadrants  removed  so  as 
to   show  the  suspended 
aluminium  needle. 

A  similar  form  of  in- 
strument is  shown  in  Fig. 

185,  with  all  the  quad- 
rants in  place,  and  cov- 
ered by  a  glass  shade. 

To  use  the. instrument, 
the  sectors  are  connected 
with  the  source  whose 
difference  of  potential  is 
to  be  measured,  and  the 
deflection  of  the  needle 
observed,  through  a  tele- 
scope, by  means  of  a  spot 
of  light  reflected  from  a 
mirror  attached  to  the  upper  part  of  the  needle. 

Sometimes  the  segments  are  made  in  tjie  shape  of  a  cylin- 
der, and  the  needle  in  the  shape  of  a  suspended  rectangle. 
Electro-motive  Force,  or  E.  M,  F,— The  force  that 
causes  electricity  to  move, 


243  A  DICTIONARY  OF  ELECTRICAL 

The  term  electro-motive  force  is  generally  written  thus  : 
E.M.F. 

The  electro-motive  force  is  due  to  a  difference  of  electrical 
level  or  potential.  In  the  current  that  results,  the  flow  is  as- 
sumed to  be  directed  from  the  higher  to  the  lower  level,  just 
as  in  the  case  of  liquids.  (See  Potential.) 

The  term  electro-motive  force  should  not  be  used  as  entirely 
synonymous  with  difference  of  potential.  The  electro-motive 
force  of  any  source  is  only  correctly  applied  to  the  total  gen- 
erated difference  of  potential.  Anything  less  than  this  at 
various  parts  of.the  circuit  is  more  correctly  spoken  of  as  a 
difference  of  potential. 

The  unit  of  electro-motive  force  is  the  volt.     (See  Volt.) 


fig.  186. 

Electro-Motive  Force,  Average (See  Aver- 
age Electro-Motive  Force.) 
Electro-HIotive  Force,   Counter  or   Back 

—(See  Counter  Electro-Motive  Force.) 

Electro-Holograph. — An  apparatus  invented  by  Edison 
whereby  the  friction  of  a  platinum  point  against  a  rotating 
cylinder  of  moist  chalk  is  reduced  by  the  passage  of  an  electric 
current, 


WORDS,  TERMS  AND  PHRASES.  243 

This  result  is  due  to  an  electrolytic  action  at  the  points  of 
contact,  varying  the  friction. 

Edison  has  constructed  a  telephone  on  this  principle.  The 
electro-motograph,  though  less  certain  in  its  action  than  an 
electro-magnet,  may  repla.ce  it  in  certain  electric  apparatus. 

The  detailed  construction  of  the  electro-motograph  may  be 
understood  from  an  inspection  of  Fig.  186. 

The  lever  A,  pivoted  with  a  universal  joint  at  C,  has  a 
metallic  point  at  its  free  extremity  F,  resting  on  a  strip  of 
moistened  paper  N,  and  held  against  it  with  some  pressure 
by  the  action  of  the  spring  S.  The  paper  N  rests  on  the 
metallic  drum  G,  over  which  it  is  moved  in  the  direction  of 
the  arrow  on  the  rotation  of  the  drum  by  clockwork.  A 
spring  R  acts  to  move  the  lever  A  in  a  direction  opposite  to 
that  in  which  it  tends  to  move  by  the  rotation  of  the 
drum  G. 

The  main  battery  L  is  connected  at  its  negative  pole  to 
the  point  F  and  at  its  positive  pole,  through  the  key  K,  to 
the  metallic  drum  G.  The  local  battery  L  B,  is  connected 
through  the  sounder  X  to  the  contacts  D  and  X. 

When  the  key  K  is  open,  the  friction  of  F  on  the  paper, 
N,  is  sufficient  to  move  the  lever  A  to  the  right  so  as  to  close 
the  circuit  of  the  local  battery  ;  but  when  the  key  K  is  de- 
pressed, the  current  of  L,  passing  through  the  paper,  decom- 
poses the  chemicals  with  which  it  is  moistened,  lessens  the 
friction  of  the  point  F,  and  permits  the  spring  B,  to  draw 
the  iever  A,  to  the  left,  thus  opening  the  circuit  of  the  local 
battery  L  B. 

The  movements  of  the  key  are  therefore  reproduced  by  the 
armature  of  the  electro-magnet  X. 

Electro-Muscular    Excitation.— In  electro  therapeu- 
tics the  galvanic  or  faradic  excitation  of  the  muscle,  or  its  ex- 
citation by  the  continuous  currents  of  a  voltaic  battery,  or  the 
alternating  currents  of  an  induction  coil. 
Electro-Optics.— (See  Optics,  Electro.) 


244 


A  DICTIONARY  OF  ELECTRICAL 


Electrophorus. — An  apparatus  for  the  production  of  elec- 
tricity by  electrostatic  induction.  (See  Induction,  Electrostatic. ) 
A    disc  of    vulcanite,   or  hard  rubber  B,  contained    in  a 
metallic  form,  is  rubbed  briskly  by  a  piece  of  cat's  skin  and 
the  insulated  metallic  disc  A,  is  placed  on 
the  centre  of  the  vulcanite  disc,  as  shown 
in  Fig.  187. 

The  negative  charge  produced  in  B  by 
the  friction,  produces  by  induction  a  pos- 
itive charge  on  the  part  of  A  nearest  it, 
and  a  negative  charge  on  the  part  furthest 
from  it. 

In  this  condition,  if  the  disc  be  raised 
from  the  plate  by  means  of  its  insulating 
Fig.  187.  handle,  as  shown  in  Fig.  188,  no  electrical 

effects  will  be  noticed,  since  the  two  opposite  and  equal  charges 
unite  and  neutralize  each  other.  If,  however,  the  disc  A  be  first 
touched  by  the  finger,  and  then  raised 
from  the  disc  B,  it  will  be  found  to  be 
positively  charged. 

Electro-Physiology.  —  The  study 
of  the  electric  phenomena  of  living  an- 
imals and  plants. 

Living  animals  and  plants  present 
electric  phenomena,  due  to  the  electricity 
naturally  produced  by  them.  It  is  the 
study  of  electro-physiology  to  ascertain 
the  causes  and  effects  of  these  phe- 
nomena, fig.  188. 

Electro-Plating.— The  process  of  covering  any  electri- 
cally conducting  surface  with  a  metal  by  the  aid  of  the  elec- 
tric current. 

By  the  aid  of  electro-plating,  the  baser  metals  are  covered 
with  silver,  nickel,  or  copper,  or  with  any  other  metal,  such  as 
gold,  or  platinum. 


WORDS,  TERMS  AND  PHRASES.  345 

The  process  of  electro-plating  is  carried  on  as  follows  : 

The  object  to  be  plated  is  connected  with  the  negative  termi- 
nal of  a  battery  and  placed  in  a  solution  of  the  metal  with 
which  it  is  to  be  plated,  opposite  a  plate  of  that  metal  con- 
nected to  the  negative  terminal  of  the  battery.  If,  for  ex- 
ample, the  object  is  to  be  plated  with  copper  it  is  placed  in  a 
solution  of  copper  sulphate  or  blue  vitriol,  opposite  a  plate  of 
copper.  By  this  arrangement  the  object  to  be  plated  forms 
the  kathode  of  the  plating  bath,  and  the  plate  of  copper 
forms  the  anode. 

On  the  passage  of  the  current  the  copper  sulphate  (Cu  SO4)  is 
decomposed,  metallic  copper  being  deposited  in  an  adherent 
layer  on  the  articles  attached  to  the  kathode,  and  the  acid  rad- 
ical (SO4)  appearing  at  the  anode,  where  it  combines  with  one 
of  the  atoms  of  the  copper  plate.  Since  for  every  molecule  of 
copper  sulphate  decomposed  in  the  electrolyte,  a  new  mole- 
cule of  copper  sulphate  is  thus  formed,  by  the  gradual  solu- 
tion of  the  copper  anode,  the  strength  of  the  solution  in  the 
bath  is  maintained  as  long  as  any  of  the  copper  plate  remains 
at  the  anode,  and  the  ordinary  activity  of  the  cell  is  not 
otherwise  interfered  with. 

When  any  other  metals  such  as  gold,  silver,  or  nickel,  for  ex- 
ample, are  to  be  deposited,  suitable  solutions  of  their  salts  are 
placed  in  the  bath,  and  plates  of  the  same  metal  hung  at  the 
anode. 

The  character  and  coherence  of  the  metallic  coatings  thus 
obtained  depend  on  the  nature  and  strength  of  the  plating 
bath,  and  on  the  density  of  the  current  employed.  The  size 
and  position  of  the  anode,  as  compared  ^ith  that  of  the  objects 
to  be  plated,  must  therefore  be  carefully  attended  to,  as  well 
as  the  strength  of  the  metallic  solution  and  the  current 
strength  passing.  (See  Density  of  Current.) 

Fig.  189.  shows  a  bath  arranged  for  silver-plating. 

The  anode  consists  of  a  plate  of  silvei*.  The  spoons,  forks, 
etc.,  to  be  plated  are  immersed  in  a  suitable  silver  solution 
and  connected  with  the  kathode. 


24$  A  t>ICf iONARY  OF  ELECTRICAL 

The  electrotyping  process  is  employed  for  the  production  of 
electrotype  plates.  It  was  called  by  Jacobi,  the  galvano- 
plastic  process.  The  term  electrotyping  is  however  more  gen- 
erally adopted. 

Electro-Pneumatic  Signals. — (See  "  Signals,"  Electro- 
Pneumatic.  ) 

Electropoion  Liquid.— A  battery  liquid  consisting  of 
one  pound  of  bichromate  of  potash  dissolved  in  ten  pounds  of 
water,  to  which  two  and  one-half  pounds  of  commercial  sul- 
phuric acid  have  been  gradually  added. 

This  liquid  is  employed  with  the  carbon-zinc  cell  or  the  bi- 
chromate of  potash  cell. 


Fig.  189. 

Electro -Puncture,  or  Galvano  -  Puncture.— The 

application  of  electrolysis  to  the  treatment  of  aneurisms,  or 
diseased  growths. 

The  blood  is  decomposed  by  the  introduction  of  a  fine  plati- 
num needle  connected  with  the  anode  of  a  battery  and  insu- 
lated, except  near  its  point,  by  a  covering  of  vulcanite. 

The  kathode  is  a  sponge  covered  metallic  plate. 


WORDS,  TERMS  AtfD  PHRASES. 


247 


Electro-Receptive  Devices.— (See  Devices,  Electro- 
Receptive.) 

Electroscope. — An.  apparatus  for  showing  the  presence 
of  an  electric  charge,  or  for  determining-  its  sign,  whether 
positive  or  negative,  but  not  for  measuring  the  value  of  the 
charge. 

In  the  gold  leaf  electroscope,  two  gold  leaves,  n  n,  Fig.  190, 
suspended  near  one  another,  show  by  their  repulsion  the 
presence  of  a  charge.  Two  pith  balls  may  be  used  for  the 
same  purpose. 


9.  Fig.  191. 

To  use  an  electroscope  for  deter  mining  the  signot  a  charge, 
the  gold  leaves  or  pith  balls  are  first  slightly  repelled  by  a 
charge  of  known  name,  as,  for  example,  positive,  applied  to 
the  knob  C.  They  are  then  charged  by  the  electrified  body 
whose  charge  is  to  be  determined.  If  they  are  further  re- 
pelled, its  charge  is  positive.  If  they  are  first  attracted  and 
afterwards  repelled,  its  charge  is  negative. 

Similarly,  if  the  pith  balls,  B  B,  shown  in  Fig.  191,  re- 
pelled by  a  known  charge,  be  approached  by  a  similar  charge 
in  S,  they  will  at  once  be  still  further  repelled,  as  shown  by 
the  dotted  lines. 

Two  posts  B,  Fig.  190,  connected  with  the  earth,  increase  the 
amount  of  divergence  by  induction. 


S48 


A  DICTIONARY  OP  ELECTRICAL 


Electroscope,  Condensing, Volta's.— An 

electroscope  employed  for  the  detection  of  feeble  charges,  the 
leaves  of  which  are  charged  by  means  of  a  condenser. 

The  condensing  electroscope,  Fig.  192,  is  formed  of  two  me- 
tallic plates,  placed  at  the  top  of  the  instrument,  and  separated 
by  a  suitable  dielectric.     The  upper  plate  P,  is  removable  by 
means  of  the  insulated  handle  G. 
To  employ  the  electroscope,  as  for 
example,  to  detect  the  free  charge  in 
an  unequally  heated  crystal  of  tour- 
maline the  crystal  is  touched  to  the 
lower  plate,  while  the  upper  plate  is 
connected  to  the  ground  by  the  finger. 
On  the  subsequent  removal  of  the 
upper  plate,    an  enormous  decrease 
ensues  in  the  capacity  of  the  conden- 
ser,  and  the  charge  now  raises  the 
potential    of   the   lower   plate,    and 
causes  a  marked  divergence  of  the 
Fig.  192.  leaves,  L  L.     (See  Pyro-Electricity.) 

Electroscope,    Quadrant  Henley's.— An 

electroscope  sometimes  employed  to  indicate  large  charges  of 
electricity. 

A  pith  ball  placed  on  a  light  arm  A,  of  straw  or  other 
similar  material,  Fig.  193,  is  pivoted  at  the  centre  of  a  gradu- 
ated circle  B.  The  arm  C  is  attached  by  means  of  the  screw 
to  the  prime  conductor  of  an  electric  machine.  The  similar 
charge  imparted  to  A  by  contact  with  C,  causes  a  repulsion 
which  may  be  measured  on  the  graduated  arc. 

This  instrument  approaches  the  electrometer  in  its  opera- 
tion, since  by  its  means  simple  measurements  may  be  made  of 
the  value  of  the  repulsion.  It  should  not,  however,  be  con- 
founded with  the  quadrant  electrometer.  (See  Electrometer, 
Quadrant.) 
Electrostatic  Field.— (See  Field,  Electrostatic.) 


WORDS,  TERMS  ASTD  PHRASES.  249 

Electrostatic     Induction.— (See    Induction,   Electro- 
static.) 

Electrostatic  Induction  Machines. — (See  Machines, 
Electrostatic  Induction.) 

Electrostatic  Lines  of  Force. — (See 
Lines  of  Force,  Electrostatic.) 

Electrostatic  Stress.— The  force,  or 
pressure  in  an  electric  field  which  produces 
a  strain  or  deformation  in  a  piece  of  glass  or 
similar  body  placed  therein.  (See  Optical 
Strain,  Electrostatic.) 

Electrostatics. — That  branch  of  electric 
science  which  treats  of  the  phenomena  and 
measurement  of  electric  charges. 

The  principles  of  electrostatics  are  em- 
braced in  the  following  laws,  viz. : 

(1)  Charges  of  like  name,  t.  e.,  either  pos- 
itive or  negative,  repel  each  other.     Charges 
of  unlike  name  attract  each  other. 

(2)  The  forces  of  attraction,  or  repulsion 
between  two  charged  bodies  are  directly  pro- 
portional to  the  product  of  the  quantities  of 
electricity  possessed  by  the  bodies  and  in- 
versely proportional  to  the  square  of  the  dis- 
tance between  them. 

These  laws  can  be  demontsrated  by  the 
use  of  Coulomb's  torsion  balance.  (See  Bal- 
ance, Torsion.)  ^,.  lgg 

Electro-Therapeutic  Bath.— (See  Bath,  Electro-Ther- 
apeutic.) 

Electro-Therapeutics,  or  Electro-Therapy.— The 

application  of  electricity  to  the  curing  of  disease.     (See  Elec- 
ro-Biology). 


250  A  DICTIONARY  OF  ELECTRICAL 

Electro-Therapy,  or  Electro-Therapeutics.— The 

application  of  electricity  to  the  treatment  of  disease. 

Electrotonus.— A  condition  of  altered  functional  activity 
which  occurs  in  a  nerve  when  subjected  to  the  action  of  an 
electric  current. 

This  alteration  may  consist  in  either  an  increased  or  a 
decreased  functional  activity.  The  decreased  functional 
activity  occurs  in  the  neighborhood  of  the  anode  or  the  posi- 
tive terminal,  and  is  called  the  anelectrotonic  state.  The  in- 
creased functional  activity  occurs  in  the  neighborhood  of  the 
kathode,  or  the  negative  terminal,  and  is  called  the  kathelec- 
trotonic  state.  (See  Anelectrotonous.  Kathelectrotonous.) 

Electrotyping,  or  the  Electrotype  Process.— Ob- 
taining casts  or  copies  of  objects  by  depositing  metals  in 
moulds  by  the  agency  of  electric  currents. 

The  moulds  are  made  of  wax,  or  other  substance,  rendered 
conducting  by  mixing  with  powdered  plumbago. 

The  mould  is  connected  with  the  negative  battery  terminal, 
and  placed  in  a  metallic  solution,  generally  copper  sulphate, 
opposite  a  plate  of  the  same  metal,  connected  with  the  positive 
battery  terminal.  As  the  current  passes,  the  metal  is  de- 
posited on  the  mould  at  the  kathode,  and  dissolved  from  the 
metallic  plate  at  the  anode,  thus  maintaining  constant  the 
strength  of  the  bath. 

Element,  Negative (See  Couple,  Voltaic.) 

Element  of  Current. — (See.  Current,  Element  of.) 

Element,  or  Elementary  Matter.— Matter  which  can- 
not be  decomposed  into  simple  matter. 

Matter  that  is  formed  or  composed  of  but  one  kind  of  atoms. 

Oxygen  and  hydrogen  are  elements,  or  varieties  of  ele- 
mentary matter.  They  cannot  be  decomposed  into  anything 
but  oxygen  or  hydrogen.  Water,  on  the  contrary,  is  com- 
pound matter,  since  it  can  be  decomposed  into  its  constituent 
parts,  oxygen  and  hydrogen. 


WORDS,  TERMS  AKD  PHRASES. 


251 


There  are  about  seventy  well  known  elements,  some  of 
which  are  very  rare,  occurring  in  extremely  small  quantities. 

The  evidence  of  the  true  elementary  condition  of  many  of 
the  elements  is  based,  to  a  great  extent,  on  the  fact  that  so 
far  they  have  resisted  all  efforts  made  to  decompose  them 
into  simpler  substances.  We  should  bear  in  mind,  however, 
that  until  Davy's  use  of  the  voltaic  battery,  potash,  soda  and 
many  other  similar  compounds  were  regarded  as  true  ele- 
ments. It  is  therefore  not  improbable  that  many  of  the  now 
so-called  elements,  may  hereafter  be  decomposed  into  simpler 
constituents. 

Element,  Positive (See  Couple,  Voltaic.) 

The  following  tables  give  the  names,  chemical  symbols, 
equivalents  and  specific  gravities  of  the  principal  elements. 
Simple  Substances,   with  their  Symbols,   Equivalents    and 
Specific  Gravities. 


NAME. 

Symbol. 

Equiv. 

Sp.  Grav. 

Aluminium  

Al 

13.7 

2.56 

Antimony 

Sb 

64.6 

6.70 

Arsenic  

As 

37.7 

5.70 

Bismuth 

Bi 

71.5 

9.82 

Bromine  _.  

Br 

78.4 

3.00 

Cadmium  

Cd 

55.8 

8.65 

Calcium 

Ca 

20.5 

1.58 

Carbon 

c 

6.1 

3.50 

Chlorine.  

Cl 

35.5 

2.44 

Cobalt 

Co 

29  5 

8.53 

Copper 

Cu 

31.7 

8.80 

Fluorine 

F 

18.7 

1.32 

Gold  (aurum)  

Au 

196.6 

19.30 

Hydrogen 

H 

1.0 

0.069 

Iodine 

I 

126.5 

4.94 

Indium 

Ir 

98.5 

18.68 

Iron 

Fe 

28.0 

7.75 

Lead 

Pb 

103.7 

11.35 

Magnesium 

Mg 

12.7 

1.75 

Manganese  

Mn 

26.0 

8.00 

A  DICTIONARY  OF  ELECTRICAL 


NAME. 


Symbol.  I   Equiv. 


Sp.  Grav. 


Mercury _ Hg 

Molybdenum Mo 

Nickel Ni 

Nitrogen N 

Osmium  _.. Os 

Oxygen O 

Palladium Pd 

Phosphorus * _ P 

Platinum Pt 

Potassium K 

Rhodium • R 

Selenium Se 

Silver Ag 

Sodium Na 

Strontium Sr 

Sulphur S 

Tellurium Te 

Tin Sn 

Titanium Ti 

Tungsten W 

Uranium U 

Zinc ...  Zn 


200.0 
47.9 
29.5 
14.2 
99.7 
8.0 
53.3 
15.9 
98.8 
39.2 
52.2 
40.0 

108.3 
23.5 
43.8 
16.1 
64.2 
58.9 
24.5 
92.0 
60.0 
32.3 


13.50 
8.60 
8.80 
0.972 

10.00 
1.102 

11.35 
1.77 

21.50 
0.865 

11.00 
4.5 

10.5 
0.972 
2.54 
1.99 
6.30 
7.29 
5.28 

17.00 

10.15 
7.00 


Element,  Thermo-EIectric 


Clark  &  Sabine. 
— One  of  the  metals 


or  substances  which  forms  a  thermo-electric  couple.  (See  Cou- 
ple, Tliermo-Electric.) 

Element,  Voltaic One  of  the  metals  or  sub- 
stances which  forms  a  voltaic  couple.  (See  Couple,  Voltaic.) 

Elements,  Electrical  Classification  of A 

classification  of  the  elements  into  two  groups  or  classes  ac- 
cording to  whether  they  appear  at  the  anode  or  kathode  when 
electrolyzed. 

The  chemical  elements  may  be  arranged  into  electro-positive 
and  electro-negative  according  to  whether,  during  electrolysis, 
they  appear  at  the  negative  or  positive  terminal  of  the  source. 

The  electro-positive  elements  or  radicals  are  called  kathions, 


WORDS,  TERMS  AND  PHRASES.  353 

and  appear  at  the  kathode  or  electro-negative  terminal.  The 
electro-negative  elements  are  called  unions,  and  appear  at  the 
anode  or  the  electro-positive  terminal.  (See  Ions.) 

The  metals  generally  are  electro-positive  ;  oxygen,  chlorine, 
iodine,  fluorine,  etc.,  are  electro-negative. 

Elongation,  Magnetic  — An  increase  in  the 

length  of  a  bar  of  iron  on  its  magnetization. 

This  increase  in  length  is  thought  to  greatly  strengthen 
Hughes'  theory  of  magnetism.  (See  Magnetism,  Hughes' 
Theory  of.) 

Embosser,  Telegraphic An  apparatus  for  re- 
cording a  telegraphic  message  in  raised  or  embossed  characters. 

E.  M.  F.— A  contraction  generally  used  for  the  word 
electro-motive  force. 

Energy. — The  power  of  doing  work. 

The  amount  of  work  done  is  measured  by  the  product  of  the 
force,  and  the  space  through  which  it  moves.  Thus  one 
pound  raised  vertically  through  ten  feet,  ten  pounds  raised 
through  one  foot,  or  five  pounds  raised  through  two  feet,  all 
represent  the  same  amount  of  work,  viz.,  ten  foot  pounds. 

If  a  weight  of  ten  pounds  be  raised  through  a  vertical 
height  of  one  foot,  by  means  of  a  string  passing  over  a  pulley, 
there  will  have  been  expended  an  amount  of  energy  repre- 
sented by  the  work  of  ten  foot  pounds.  If  the  weight  be  pre- 
vented in  any  way  from  falling,  as  by  tying  the  string,  it  will 
have  stored  in  it  an  amount  of  energy  equal  to  ten  foot 
pounds,  and  if  permitted  to  fall,  is  capable  of  doing  an 
amount  of  work  which,  leaving  out  air  resistance  and  friction, 
is  exactly  equal  to  that  expended  in  raising  it  to  the  position 
from  which  it  falls,  viz.,  ten  foot  pounds  of  work. 

Energy,  Actual, Kinetic  Energy,  Energy  of 

Motion.— Energy  employed  in  doing  work,  or  the  power  of. 
doing  work  possessed  by  bodies  that  are  iu  jnotiQB, 


254  A  DICTIONARY  OP  ELECTRICAL, 

Energy,  Atomic  or  Chemical  Potential The 

potential  energy  possessed  by  the  elementary  chemical  atoms. 
(See  Energy,  Potential.') 

Energy,  Conservation  of (See  Conservation 

of  Energy.} 

Energy,  Degradation  of (See  Degradation  of 

Energy.) 

Energy,  Electric The  power  which  electricity 

possesses  of  doing  work. 

In  the  case  of  a  liquid  surface  at  different  levels,  the  liquid 
at  the  higher  level  possesses  a  certain  amount  of  potential 
energy  measured  by  the  quantity  of  the  liquid  at  the  higher 
level,  and  the  excess  of  its  height  over  that  of  the  lower  level ; 
or,  on  the  difference  of  level  between  them.  This  difference  of 
level  will  produce  a  current  from  the  higher  to  the  lower  level, 
and  during  the  passage  of  the  current,  potential  energy  will 
be  lost,  and  a  certain  amount  of  work  will  be  done. 

In  the  case  of  electricity,  the  difference  of  electric  level  or 
potential,  between  any  two  points  of  a  conductor,  causes  an 
electric  current  to  flow  between  these  points  from  the  higher 
to  the  lower  electric  level,  during  which  electric  potential 
energy  is  lost,  and  work  is  accomplished  by  the  current.  (See 
Potential.) 

The  amount  of  the  electric  work  is  measured  by  the  quantity 
of  electricity  that  flows,  multiplied  by  the  difference  of  poten- 
tial under  which  it  flows.  (See  Joule,  or  Volt-Coulomb.) 

Electric  energy,  however,  is  generally  measured  in  electric 
power,  or  rate  of  doing  electric  work. 

Since  an  ampere  is  one  coulomb  per  second,  if  we  measure 
the  difference  of  potential  in  volts,  the  product  of  the  amperes 
by  the  volts  will  give  the  electrical  power  in  volt-amperes,  or 
watts,  or  units  of  electric  power.  C  E  =  The  Watts.  (See 
Amptre.  Volt.  Watt.) 

One  horse-power  equals  550  foot  pounds  per  second.    One 


WORDS,  TERMS  AND  PHRASES.  255 

watt  or  volt-ampere  =     ^  of  a  horse-power,  or  one  horse- 
power equals  746  volt-amperes  or  watts,  therefore  : 

The  current  in  amperes,  multiplied  by  the  difference  of  po- 
tential in  volts,  divided  by  746,  equals  the  rate  of  doing  work 
in  horse-power. 

Thus,  if  .7  ampere  is  required  to  operate  a  16  candle,  110 
!  volt,  incandescent  lamp,  it  requires  4.8  watts  per  candle. 
One  Watt  =  44.2394  foot-pounds  per  minute. 
One  Watt  =  .737324  foot-pounds  per  second. 
The  Heat  Activity,  or  the  heat  per  second  produced  by  an 
electric  current,  is  also  proportional  to  the  product  C  E,  or  the 
watts,  for  the  heat  is  proportional  to  the  square  of  the  current 
in  amperes  multiplied  by  the  resistance  in  ohms,  or  C8  R  = 
the  Heat.     (See  Calorimeter,  Electric.) 
By  Ohm's  Law  (See  Ohm's  Law), 

E 
C  =  —    (1),     or  C  R  =  E  ,    (2), 

R 
but  the  electric  power  or  the  watts  =  C  E        (3). 

If,  now,  we  substitute  the  value  of  E,  taken  from  equation 
(2)  in  equation  (3)  we  have 

CE  =  CXCR  =  C*R; 

therefore  C8  R  =  watts. 

To  determine  the  heating  power  of  a  current  in  small  cal- 
ories, calling  H,  the  amount  of  heat  required  to  raise  1 
gramme  of  water  through  1°  Cent.,  and  C,  the  current  in 
amperes. 

H  =  Cs  R  X  .24. 
Or,  for  any  number  of  seconds,  t, 

H  =  C2  Ht  X  .24, 

Therefore,  one  watt  =  .24  calories  per  second.     (See  Calorie.) 
But  from  Ohm's  law, 

E 
C  =  -        <„, 

and  the  formula  for  electric  power  or  the  watts  =  C  E  .      (2) 


256  A  DICTIONARY   OP  ELECTRICAL 

By  substituting  in  equation  (2)  and  the  value  of  C  in  equation 

(1), 

E       E8 
C  E  =  E  X  —  =  —  =  watts. 

R        R 

That  is  to  say,  the  electric  power,  in  any  part  of  a  circuit 
varies  directly  as  the  square  of  the  electro-motive  force. 

"We  therefore  have  three  expressions  for  the  value  of  the 
watt  or  the  unit  of  electric  power,  viz. : 
C  E  =  watts.         (1) 
C8  R  =  watts.        (2) 
E2 

—  =  watts.  (3) 

R 

(1)  C  E  =  Watts ;  or  the  electric  power  is  proportional  to 
the    product   of    the    quantity    of    electricity  per    second, 
that  passes,  in  amperes,  and  the  difference  of  electric  poten- 
tial or  level,  through  which  it  passes,  in  volts. 

(2)  C8  R  =  Watts ;   or  the  electric  power  varies  directly  as 
the  resistance  R,  when  the  current  is  constant,  or  as  the 
square  of  the  current,  if  the  resistance  is  constant.     That  is 
to  say,  if  with  a  given  resistance,  the  power  of  a  given  current 
has  a  certain  value,  and  the  current  flowing  through  this  same 
resistance  be  doubled,  the  power  is  four  times  as  great ,  or  is 
as  the  square  of  the  current. 

E8 

(3)  —  =  Watts,  or  the  electric  power  is  inversely  as  the  re- 
ft 

sistance  R,  when  the  electro-motive  force  is  constant. 

A  circuit  of  one  ohm  resistance  will  have  a  power  of  one  watt, 
when  under  an  electric  motive  force  of  one  volt,  since  it  would 
then  have  a  current  of  one  ampere  flowing  through  it,  and 
C  E  =  1.  If,  however,  the  resistance  be  halved  or  becomes  .5 
ohm,  then  two  amperes  pass,  or  the  power  equals  2  watts. 

The  power  varies  as  the  square  of  the  electro-motive  force 
in  any  part  of  a  circuit,  when  the  resistance  is  constant  in 


WORDS,  TERMS  AND   PHRASESv  257 

that  part.  Thus  2  amperes,  and  2  volts,  in  a  circuit  of  one 
ohm  resistance,  give  a  power,  C  E  =  3  X  3  —  4  watts.  If  now, 
R,  remaining1  the  same,  the  electro-motive  force  be  i-aised  to  4 
volts,  then  since  E  is  doubled,  C,  or  the  amperes  are  doubled, 

E2     16 

and  CXE-4X4  =  16  watts,  or  —  =  —  =  16. 

B       1 

Energy,  Electric  Traii*mi.««iioii  of —The 

transmission  of  mechanical  energy  between  two  distant 
points  connected  by  an  electric  conductor,  by  converting  the 
mechanical  energy  into  electrical  energy  at  one  point,  send- 
ing the  current  so  produced  through  the  conductor,  and  recon- 
verting the  electrical  into  mechanical  energy  at  the  other 
point. 

A  system  for  the  electric  transmission  of  energy  embraces  : 

(1)  ^i  Conducting  Circuit  between  two  stations. 

(2)  An  Electric  Source,  or  battery  of  electric  sources,  or 
machines,  at  one  of  the  stations,  generally  in  the  form  of  a 
dynamo-electric  machine,  for  converting  mechanical  enei'gy 
into  electric  energy. 

(3)  Electro-Receptive  Devices,  generally  electric  motors,  at 
the  other  station  for  reconverting  the  electric  into  mechanical 
energy.    (See  Motors,  Electro-Magnetic.) 

Energy,  Potential,  Energy  of  Position, 

Static  Energy,  or  Energy  of  Stress.— Stoi*ed  energy ; 
potency  or  capability  of  doing  work. 

The  capacity  for  doing  work  possessed  by  a  body  at  rest, 
arising  from  its  position  as  regards  the  earth,  or  from  the  pos- 
ition of  its  atoms  as  regards  other  atoms. 

A  pound  of  coal  if  raised  vertically  one  foot,  possesses,  as  a 
mere  weight,  an  amount  of  energy  capable  of  doing  an  amount 
of  work  equal  to  one  foot  pound.  The  atoms  of  carbon,  how- 
ever, of  which  it  is  composed,  have  been  raised  or  separated 
from  those  of  oxygen,  or  some  other  elementary  substance, 
and  when  the  coal  is  burned,  or  the  cai'bon  atoms  fall  towards 


258  A  DICTIONARY  OP  PXECTRICAL 

the  oxygen  atoms  (i.  e.,  unite  with  them),  the  coal  gives  up 
the  potential  energy  of  its  atoms  in  the  form  of  heat. 

All  elementary  substances  possess  in  the  same  way  atomic, 
or  chemical  potential  energy,  or  the  energy  with  which  they 
tend  to  fall  together.  This  energy  varies  in  amount  in  differ- 
ent elements  and  becomes  kinetic,  as  heat,  on  combination 
with  other  elements. 

Engine,  Electro-Magnetic  --  A  motor  whose 
driving  power  is  electricity.  (See  Motor,  Electric.) 


,.  Acoustic  --  Engraving  by  the  human 
voice. 

In  the  Phonograph,  Oraphophone,  and  Gramophone,  a  dia- 
phragm is  set  in  vibration  by  the  speaker's  voice  so  that 
it  cuts  or  engraves  a  record  of  its  to-and-fro  movements  on  a 
sheet  of  tin  foil,  on  a  cylinder  of  hardened  wax,  or  on  a 
specialty  coated  plate  of  metal  or  glass.  This  record  is  em- 
ployed in  order  to  reproduce  the  speech.  (See  Phonograph.) 

Engraving,  Electric  --  -  or  Electro-Etching. 

—  A  method  for  electrically  etching  or  engraving  a  metallic 
plate  by  covering  it  with  wax,  tracing  the  design  on  the  wax 
so  as  to  expose  the  metal,  connecting  it  with  the  positive  ter- 
minal of  a  battery,  and  placing  it  in  a  bath  opposite  another 
plate  of  metal. 

By  the  action  of  electrolysis  the  metal  is  dissolved  from  the 
exposed  portions  and  deposited  on  the  plate  connected  with 
the  other  terminal  of  the  battery.  (See  Electrolysis.) 

By  connecting  the  waxed  plate  to  the  negative  terminal, 
the  metal  will  be  deposited  on  the  exposed  portions,  thus  pro- 
ducing the  design  in  relief.  This  latter  method  is  not,  how- 
ever, apt  to  produce  a  sufficiently  uniform  deposit  to  enable 
the  plate  so  formed  to  be  used  for  printing  from. 

Entropy.  —  In  thermo-dynamics  the  non-available  enepgy 
in  any  system.  (Ciausius  and  Mayer.) 


WORDS.  TERMS  AND  PHRAftES.  259 

The  available  energy  in  any  system.  (Tait,  Thomson,  and 
MaxweB.) 

As  will  bo  noticed  this  term  is  used  in  entirely  different  and 
opposite  senses  by  different  scientific  men.  The  latter  sense 
is,  perhaps,  the  one  most  generally  taken. 

Heat  energy  is  available  for  doing1  useful  external  work 
Only  when  the  source  of  heat  is  hotter  than  surrounding 
bodies,  that  is,  when  the  heat  is  transferred  from  a  hotter  to  a 
colder  body.  When  all  bodies  acquire  the  same  temperature 
no  more  external  work  can  be  done  by  them.  In  the  various 
transformations  of  energy  some  of  the  energy  is  converted 
into  heat,  and  this  heat  is  gradually  diffused  through  the 
universe  and  thus  becomes  non-available  to  man.  There- 
fore, the  entropy  of  our  earth  is  decreasing. 

"Entropy,  in  Thermodynamics,"  says  Maxwell,  "is  a 
quantity  relating  to  a  body  such  that  its  increase  or  diminu- 
tion implies  that  heat  has  entered  or  left  the  body.  The 
amount  of  heat  which  enters  or  leaves  the  body  is  measured 
by  the  product  of  the  increase  or  diminution  of  entropy  into 
the  temperature  at  which  it  takes  place." 

Entropy,  Electric A  term  proposed  by  Maxwell 

in  thermo-electric  phenomena  to  include  the  doctrine  of  en- 
tropy in  electric  science. 

"  When  an  electric  current,"  says  Maxwell,  "passes  from 
one  metal  to  another  heat  is  emitted  or  absorbed  at  the  junc- 
tion of  the  metals.  We  should,  therefore,  suppose  that  the 
electric  entropy  has  diminished  or  increased  when  the  elec- 
tricity passes  from  one  metal  to  the  other,  the  electric  entropy 
being  different  according  to  the  nature  of  the  medium  in 
which  the  electricity  is,  and  being  affected  by  its  temperature, 
stress,  strain,  etc." 

Equator,  Ocographical An  imaginary  great 

circle  passing  around  the  earth  midway  between  its  poles. 

Equator,  Magnetic The  magnetic  parallel,  or 

circle  on  the  earth's  surface  where  a  magnetic  needle  free  to 
more  stands  horizontal. 


A  DICTIONARY  OP  ELECTRICAL 


An  irregular  line  passing  around  the  earth  approximately 
midway  between  the  earth's  magnetic  poles.  (See  Dip,  Angle 
of.) 

Equator  of  Magnet. — A  point  midway  between  the  poles 
of  a  bar  magnet. 

This  term  was  proposed  by  Dr.  Gilbert.  It  is  now  almost 
entirely  displaced  by  the  term  neutral  point  or  points. 

Equipoteiitial  Surfaces.— Surfaces,  all  the  points  of 
which  are  at  the  same  electric  potential.  (See  Potential, 
Electric.) 

Electric  surfaces  perpendicular  to  the  lines  of  electric  force 
over  which  a  quantity  of  electricity,  considered  as  being  con- 
centrated   at    a  point,   may  be 
moved  without  doing  work.   (See 
Field,  Electrostatic.) 

In  electrostatics,  equipotential 
surfaces  correspond  with  a  water 
level,  over  which  a  body  may  be 
moved  horizontally  against  the 
force  of  gravity  without  doing 
any  work. 

In  the  case  of  the  charged  in- 
sulated sphere,  shown  in  the  Fig. 
194,  the  equipotential  surfaces, 
represented  by  the  circles,  are 
concentric. 


Fig.  19k. 


Equipoteiitial    Surfaces,    Magnetic 


Surfaces  surrounding  the'poles  of  a  magnet,  or  system  of  mag- 
nets, where  the  magnetic  potential  is  the  same.  (See  Poten- 
tial, Magnetic.) 

Magnetic  equipotential  surfaces  extend  in  a  direction  per- 
pendicular to  the  lines  of  magnetic  force.  (See  Field,  Mag- 
netic.) 

Therefore  work  is  required   in   order  to  move  a  unit  pole 


•WORDS,  TERMS  AND  PHRASES.  261 

across  equipotential  magnetic  surfaces,  because  in  so  doing 
it  cuts  the  lines  of  magnetic  force. 

Equipotential  surfaces,  whether  electric  or  magnetic,  cannot 
intersect  one  another  since  their  potential  is  the  same  at  all 
points. 

Equivalent,  Chemical The  quotient  obtained 

by  dividing  the  atomic  weight  of  any  elementary  substance  by 
its  atomicity.  (See  Atomic  Weight.  Atomicity.) 

The  chemical  equivalent  is  different  from  the  atomic  weight. 
The  atomic  weight  of  gold  is  196.6,  but  since  in  chemical  com- 
bination one  atom  of  gold  is  capable  of  combining  with  three 
atoms  of  hydrogen,  the  weight  of  the  gold,  equivalent  to  that 
of  one  atom  of  hydrogen  is  one-third  of  196.6,  or  65.5. 

Equivalent,  Electro-Chemical.—  A  number  represent- 
ing the  weight  of  an  elementary  substance  liberated  during 
electrolysis  by  the  passage  of  one  coulomb  of  electricity.  (See 
Electrolysis.  Coulomb.) 

It  may  be  determined  experimentally  that  one  coulomb  of 
electricity  expended  electrolytically  will  liberate  .0000105 
grammes  of  hydrogen.  Therefore  a  current  of  one  ampere, 
or  one  coulomb  per  second,  will  liberate  .0000105  gramme  of 
hydrogen  per  second.  The  number  .0000105  is  the  electro- 
chemical equivalent  of  hydrogen. 

The  electro-chemical  equivalents  of  the  other  elements 
are  obtained  by  multiplying  the  electro-chemical  equiv- 
alent of  hydrogen  by  the  chemical  equivalent  of  the  sub- 
stance. 

Thus,  the  chemical  equivalent  of  potassium  is  39.1,  therefore 
its  eleclro-clii'iiiiriil  equivalent  is  39.1  x  .0000105  =  .00041055. 
By  multiplying  the  strength  of  the  current  that  passes  by  the 
electro-chemical  equivalent  of  any  substance,  we  obtain  the 
weight  of  that  substance  liberated  by  electrolysis. 

The  following  Table  of  Electro-Chemical  Equivalents  is  col" 
from  different  authorities,  mainly  Hospitaller. 


A  DICTIONARY  OF  ELECTRICAL 


Electro- Chemical  Equivalents. 


* 

is. 

II 

Ii 

D 

ri 

S2 

ii 

NAMES  OF  ELEMENTS. 

£ 

g 

'1 

ll 

gs 

ll 

•§ 

« 

§       .0 

^     Q 

yt 

fal 

o  "*"*  £ 

_o  ^* 

1 

1 

ii! 

Iss 

Ml 

ill 

< 

K- 

0 

K 

s 

Electro-positive. 
Hydrogen 

1. 

1 

1. 

.0000105 

96,000 

.0378 

Potassium  

39.1 

1 

39.1 

.0004105 

2,455 

1.4680 

Sodium 

23. 

1 

23. 

.0002415 

4,174 

.8694 

Gold 

196.6 

65.5 

0006875 

1,466 

2.4750 

Silver 

108. 

1 

108. 

.0011340 

889 

4  0824 

Copper  (ic  salts)...  .. 

63. 

2 

81.5 

0003307 

3,079 

1.1900 

Copper  (ous  salts)  .  .- 
Mercury  (ic  salts)  

63. 
200. 

1 
2 

63. 
100. 

.0006615 
.0010500 

1,540 
960 

2.3800 
3.7800 

Mercury  (ous  salts).  . 

200. 

1 

200 

0021JOO 

480 

7.5600 

Tin  (ic  salts)  

118. 

4 

29  5 

.0003097 

3,254 

1  1149 

Tin  (ous  salts)  .  .  

118. 

2 

59. 

.0006195 

1,627 

2.2298 

Iron  (ic  salts) 

56 

4 

14. 

0001470 

6,857 

.5292 

Iron  (ous  salts)  

56. 

2 

28. 

.0002940 

3,429 

1.0584 

Nickel 

59. 

g 

29.5 

0003097 

3,254 

1.1249 

Zinc 

65. 

2 

32.5 

0003412 

2,953 

1  2283 

Lead 

207 

103  5 

.0010867 

928 

3  9041 

Electro-nega  t  ive. 
Oxygen 

16. 
35.5 

2 

1 

8. 
35.5 

.0000840 
.0003727 

Chlorine 

Iodine 

127. 

1 

127. 

.0013335 

Bromine           ..   . 

80 

80 

.0008400 

Nitrogen  .  _   

14. 

3 

4.3 

.0000490 

Equivalent  of  Heat,  INeeliaiiical (See  Me- 
chanical Equivalent  of  Heat.) 

Equivolt. — A  term  proposed  by  J.  T.  Sprague  for  the  unit 
of  electrical  energy,  applied  especially  to  chemical  decomposi- 
tion. 


WORDS,  TERMS   AND   PHRASES.  263 

Sprague  defines  equivolt  as  follows  :  "  The  mechanical 
energy  of  one  volt  electro-motive  force  exerted  under  unit 
conditions  through  one  equivalent  of  chemical  action  in 
grains." 

This  term  has  not  been  generally  accepted.  (See  Volt- 
Coulomb,  or  Joule.) 

Erg. — The  unit  of  work,  or  the  work  done  when  unit  force 
is  overcome  through  unit  distance. 

The  work  accomplished  when  a  body  is  moved  through  a 
distance  of  one  centimetre  with  the  force  of  one  dyne.  (See 
Dyne.) 

The  work  done  when  a  weight  of  one  gramme  is  raised 
against  gravity  through  a  vertical  height  of  one  centimetre, 
is  equal  to  981  ergs,  because  the  weight  of  one  gramme  is 
1  x  981  dynes,  or  981  ergs. 

The  dyne  is  the  unit  of  force,  or  a  force  capable,  after  act- 
ing for  one  second,  of  giving  a  mass  of  one  gramme  a 
velocity  of  one  centimetre  per  second.  The  weight  of  a  body 
in  dyncti,  or  the  force  with  which  it  gravitates,  is  equal  to  its 
mass  in  grammes,  multiplied  by  the  acceleration  imparted  to 
it  in  centimetres  per  second.  For  this  latitude  the  accelera- 
tion is  about  981  centimetres  per  second. 

Ergmelcr. — An  apparatus  for  measuring  in  ergs  the  work 
of  an  electric  current. 

Erg-ten. — A  term  proposed  for  ten  million  ergs  or  1  X  1010 
=  10,000,000,000. 

In  representing  large  numbers  containing  many  ciphers  ihn 
plan  is  often  adopted  of  representing  the  number  of  ciphers 
that  are  to  be  added  to  a  given  number  by  10,  with  an  exponent 
equal  to  the  number  of  ciphers.  Tims,  38  x  108  indicates  that 
38  is  to  be  followed  by  8  ciphers,  thus  3,800,000,000. 

A  negative  exponent,  as  3  X  10-8  represents  the  correspond- 
ing decimal  thus,  .00,000,003. 

1  erg  X  1010,  or  10,000,000,000  is  called  an  erg-ten.     1  X  10a 


264  A  DICTIONARY   OF  ELECTRICAL 

=  an  erg-six.  These  terms  are  not  in  general  use.  Ten 
meg-ergs  is  a  preferable  phrase  to  an  erg-ten.  (See  Meg-erg.) 

Escape,  Electric A  term  sometimes  employed 

to  indicate  the  loss  of  charge  on  an  insulated  conductor.  (See 
Leakage,  Electric.) 

Etching,  Electric (See  Engraving,  Electric.) 

Ether.— The  tenuous,  highly  elastic  fluid  that  is  assumed 
to  fill  all  space,  and  by  vibrations  or  waves  in  which  light 
and  heat  are  transmitted. 

Although  the  existence  of  the  ether  is  assumed  in  order  to 
explain  certain  phenomena,  its  actual  existence  is  very 
generally  credited  by  scientific  men,  and,  in  reality,  proofs  are 
not  wanting  to  fairly  establish  its  existence. 

Light  and  heat  are  believed  to  be  due  to  transverse  vibra- 
tions in  the  ether.  Magnetism  appears  to  be  due  to  whirls  or 
whirl-pools,  and  an  electric  current  is  believed  by  some  to  be 
due  to  ether  set  in  motion  by  differences  in  the  ether  pres- 
sures. 

It  is  not  correct  to  regard  the  luminiferous  ether  as  possess- 
ing no  weight,  or  as  being  imponderable.  Maxwell  estimates  its 

density  M  i.ooo.ooo.ooo!ooo.ooo,ooo.ooo  that  of  water-   tt 

is  very  readily  moved  or  set  into  vibration,  its  rigidity  being 
estimated  at  about  1  QQQ  OQO  QQQ  that  of  steel- 

According  to  the  speculations  of  some  physicists  the  ether 
is  not  discontinuous  or  granular,  but  is  similar  to  what  might 
be  regarded  as  an  almost  impalpable  jelly. 

Eudiometer.— A  Voltameter  in  which  separate  gradu- 
ated vessels  are  provided  for  the  reception  and  measurement 
of  the  gaseous  products  evolved  during  electrolysis.  (See 
Voltameter.) 

In  all  cases  electrodes  must  be  used  which  do  not  enter  into 
combination  with  the  evolved  gaseous  products.  In  the 
case  of  oxygen  and  hydrogen,  platinum  is  generally  used. 


WORDS,  TERMS  AND  PHRASES. 


365 


A  form  of  eudiometer  is  shown  in  Fig.  195.  Two  separate 
glass  vessels  provided  at  the  top  with  stop  cocks,  and  open  at 
their  lower  ends,  rest  in  a  vessel  of  water  A,  over  platinum 
electrodes,  connected  electrically  with  binding  posts  K,  K. 
Both  vessels  are  filled  with 
water  slightly  acidulated  with 
sulphuric  acid,  and,  when 
connected  with  a  battery  of 
sufficient  electro-motive  force, 
(not  less  than  1.45  volts),  elec- 
trolysis takes  place,  and  hy- 
drogen gas  collects  in  the 
vessel  over  the  platinum  elec- 
trode connected  with  the  neg- 
ative battery  terminal,  and 
oxygen  in  that  over  the  one 
connected  with  the  positive 
battery  terminal.  The  volume 
of  the  hydrogen  is  about  twice 
as  great  as  that  of  the  oxygen. 
(See  Water,  Electrolysis  of.) 

Evaporation  .—The 
change  from  the  liquid  to  the 
vaporous  state. 

Wet  clothes  exposed  to  the 
air  are  dried  by  the  evapora- 
tion of  the  water. 

Evaporation  is  greater : 

(1)  The  more  extended  the 
surface  exposed. 

(2)  The  higher  the  temperature  of  the  air. 

(3)  The  dryer  the  air,  or  the  smaller  the  quantity  of  vapor 
already  in  it. 

(4)  The  stronger  the  wind. 

(5)  The  smaller  the  pressure  of  the  air. 


Fig,  195. 


366  A  DICTIONARY   OF  ELECTRICAL 

Evaporation,  Electrification  by Electrifica- 
tion resulting  from  the  condensation  of  a  mass  of  vapor. 

The  free  electricity  of  the  atmosphere  is  believed  by  some 
to  be  due  to  the  condensation  of  the  vapor  of  the  air  that 
results  in  rain,  hail,  clouds,  etc.  It  is  probable,  however, 
that  the  true  effect  of  condensation  is  mainly  limited  to  the 
increase  of  a  feeble  electrification  already  possessed  by  the 
air  or  its  contained  vapor.  The  small  difference  of  potential 
of  the  exceedingly  small  drops  of  water  in  clouds,  is  enor- 
mously increased  by  the  union  or  coalescing  of  many  thous- 
ands of  such  drops  into  a  single  rain  drop.  (See  Atmospheric 
Electricity.) 

Exchange,  Telephonic System  of  — A  com- 
bination of  circuits,  switches  and  other  devices,  by  means  of 
which  any  one  of  a  number  of  subscribers  connected  with  a 
telephonic  circuit,  or  a  neighboring  telephonic  circuit  or  cir- 
cuits, may  be  placed  in  electrical  communication  with  any 
other  subscriber  connected  with  such  circuit  or  circuits. 

A  telephone  exchange  consists  essentially  of  a  multiple 
switch-board,  or  a  number  of  multiple  switch-boards,  fur- 
nished with  spring-jacks,  annunciator  drops,  and  suitable  con- 
necting cords.  A  call  bell,  or  bells,  is  also  provided.  The 
annunciator  drops  are  often  omitted.  (See  Board,  Multiple 
Switch.) 

Excitability,  Electric of  Nerve  or  Muscular 

Fibre. — The  effect  produced  by  an  electric  current  in  stimu- 
lating the  nerve  of  a  living  animal  or  producing  an  involun- 
tary contraction  of  a  muscle. 

Du  Bois-Reymond  has  shown  that  these  effects  depend  ; 

(1)  On  the  strength  of  the  current  employed,  and  that  they 
occur  only  when  the  current  begins  to  "flow,  and  when  it 
ceases  flowing,  or,  when  the  electrodes  first  touch  the  nerves, 
and  when  they  are  separated  from  it.  Subsequent  investiga- 
tion have  shown  that  this  is  true  only  for  the  frog's  nerves, 


WORDS,  TERMS  AND  PHRASES.  267 

and  is  true  for  the  human  nerves  only  in  the  case  of  moderate 
currents,  strong  currents  producing  tetanus. 

(2)  On  the  rapidity  with  which  the  current  used  readies  its 
maximum  value,  that  is,  on  the  rapidity  of  change  of  current 
density.  (See  Current  Density.) 

Excitability,  Faradic Muscular  or  nervous 

excitability  folio  wing  the  employment  of  the  rapidly  intermitt- 
ent current  produced  hy  induction  coils.  (See  Induction  Coils.) 

Faradic  excitability  is  different  from  galvanic  excitability, 
produced  by  means  of  a  continuous  voltaic  current. 

Excitation,  Electro  Muscular (See  Electro 

Muscular  Excitation.') 

Exciter  of  Field.— In  a  separately  excited  dynamo- 
electric  machine,  the  dynamo-electric  machine,  voltaic  bat- 
tery, or  other  electric  source  employed  to  produce  the  lield  of 
the  lield  magnets.  (See  Dynamo-Electric  Machines.) 

Execution,  Electric -Causing  the  death  of  a 

criminal,  in  cases  of  capital  punishment,  by  means  of  the 
electric  current. 

Electric  execution  has  been  adopted  by  the  State  of  New 
York,  in  accordance  with  the  following  law  : 

"The  Court  shall  sentence  the  prisoner  to  death  within  a 
certain  week,  naming  no  day  or  hour,  and  not  more  than 
eight  nor  less  than  five  weeks  from  the  day  of  sentence.  The 
execution  must  take  place  in  the  State  prison  to  which  con- 
victed felons  are  sent  by  the  court,  and  the  executioner  must 
be  the  agent  and  warden  of  the  prison." 

"No  newspaper  may  print  any  details  of  the  execution, 
which  is  to  be  inflicted  by  electricity.  A  current  of  electricity 
is  to  be  caused  to  .pass  through  the  body  of  the  condemned  of 
sufficient  intensity  to  kill  him,  and  the  application  is  to  be 
continued  until  he  is  dead.'' 

Exhaustion,  or  Prostration Electric.— (See 

Sun  Stroke,  Electric.) 


268  A  DICTIONARY   OF  ELECTRICAL 

Exhaustion  of  Voltaic  Cell.— The  condition  of  a 
voltaic  cell  in  which,  on  account  of  having1  all  its  active  elec- 
trolyte decomposed,  or  its  positive  plate  dissolved,  it  will 
furnish  no  difference  of  potential  and  therefore  no  current. 

An  exhausted  secondary  cell  is  revivified  or  charged,  by  the 
passage  through  it  of  a  charging  current. 

A  primary  cell  is  revivified  by  the  addition  of  fresh  electro- 
lyte or  battery  liquid,  or  a  new  positive  plate. 

Expansion,  Electric The  increase  in  vol- 
ume produced  in  a  body  on  giving  such  body  an  electric 
charge. 

A  Leyden  jar  increases  in  volume  when  a  charge  is  im- 
parted to  it.     This  result  is  due  to  an  expansion  of  the  glass 
due  to  the  electric  charge.     According  to  Qtiincke,  some  sub- 
stances, such  as  resinous  or  oily  bodies,  manifest  a  contrac- 
tion of  volume  on  the  reception  of  an  electric  charge. 
Expansion  Joints. — (See  Joints,  Expansion.) 
Exploder,    Electric • A  small  magneto- 
electric  machine  used  to  produce  the  currents  of  high  electro- 
mo-tive  force,  employed  in  the  direct  firing  of  blasts. 

Explorer,  Electric •  —  An  apparatus  oper- 
ated by  means  of  induced  currents,  and  employed  for  the  pur- 
pose of  locating  ballets  or  other  foreign  metallic  substances 
in  the  human  body.  (See  Balance,  Induction,  Hughes. ) 

Explorer,  Magnetic A  small,  Hat  coil  of  in- 
sulated wire,  used  in  the  circuit  of  a  telephone  to  determine 
the  position  and  extent  of  the  magnetic  leakage  of  a  dynamo- 
electric  machine  or  other  similar  apparatus.  (See  Magneto- 
phone.) 

Extension  Call-Bell.— (See  Bell,  Extension  Gall.) 
Extra  Currents. — Currents   produced   in  a  circuit,   by 
the  induction  of  the  current  on  itself,  on  the  opening  or  closing 
of  a  circuit.     (See  Cur  rent*,' Extra.) 
Eye,  Selenium (See  Selenium  Eye.) 


WORDS,  TERMS  AND  PHRASES. 


Fac-Simile  Telegraphy,  or  Panleleg  raplij  .—  The 

telegraphic  transmission  of  fae-simile  copies  of  drawings  or 
designs. 

In  a  system  of  fac-simile  telegraphy,  a  design  placed  at  one 
end  of  a  telegraphic  line  is  automatically  reproduced  by  elec- 
tricity at  the  other  end  of  the  line.  (See  Telegraphy,  Fac- 
simile.) 

Farad.—  The  unit  of  electric  capacity. 

As  in  gases,  a  quart  vessel  will  hold  a  quart  of  gas  under 
unit  pressure  of  one  atmosphere,  so,  in  electricity,  a  conduc- 
tor or  condenser,  whose  capacity  is  one  farad,  will  hold  a 
quantity  of  electricity  equal  to  one  coulomb,  when  under  an 
electro-motive  force  of  one  volt. 

It  may  cause  some  perplexity  to  the  student  to  understand 
why  there  should  be  in  electricity  p, 

one  unit  of  capacity  to  represent 
the  size  of  the  vessel  or  conductor, 
and  another  to  represent  the 
amount  or  quantity  of  electricity 
required  to  fill  such  vessel.  But, 
like  a  gas,  electricity  acts  as  if  it 
were  very  compressible,  so  that  I 
the  quantity  required  to  fill  any 


Fig-  m- 


condenser  will  depend  on  the  electro-motive  force  under  which 
it  is  put  into  the  conductor  or  condenser. 

A  farad  is  such  a  capacity  of  a  conductor  or  condenser  that 
one  coulomb  of  electricity  is  required  to  produce  in  it  a  differ- 
ence of  potential  of  one  volt. 

For  purposes  of  measurement,  capacities  of  conductors  are 
compared  with  those  of  condensers  whose  capacities  are 
known  in  microfarads,  or  fractions  thereof.  The  microfarad, 

or  the      AAA  AA'A  °f  a  farad>  is  used  because  of  the  very  great 

size  of  a  farad. 
Fig.  196,  shows  an  elevation  and  Fig.  197  a  plan  of  the  form 


270 


A  DICTIONARY  OP  ELECTRICAL 


often  given  to  a  standardized  condenser  or  microfarad.  The 
condenser  is  charged  by  connecting  the  terminals  of  the  elec- 
tric source  to  the  binding  posts  N  and  N.  It  is  discharged  by 
means  of  the  plug  key  P',  that 
connects  the  brass  pieces  A  and 
B,  when  pushed  firmly  into  the 
conical  space  between  them. 

The  condenser  is  made  by  plac- 
ing sheets  of  tin  foil  between 
sheets  of  oiled  silk  or  mica  in  the 
box,  and  connecting  the  alter- 
nate sheets  to  one  of  the  brass 
pieces  B,  and  the  other  set  to  the 
piece  A,  as  will  be  better  under- 
Flg.  197.  stood  from  an  inspection  of  Fig. 

198.  A  condenser  of  a  microfarad  capacity  will  contain  about 
3,600  square  inches  of  tin  foil. 

Condensers  are  generally  made  of  the  capacity  of  the  £  of  a 
microfarad.  Sometimes,  however,  they  are  made  so  that 
either  all  or  part  of  the  condenser  may  be  employed,  by  the 
insertion  of  the  different  plug  keys. 

The  form  of  condenser,  shown  in  Fig.  199  is  capable  of 
ready  division  into  five  differ-  7) 

ent  values,  viz.:  .05,   .05,   .2, 
.2,  and  .5  microfarad. 
Far  a  die  Apparatus, 

Magneto A  A 

small  magneto-electric  ma- 
chine employed  in  electro 
therapeutics  for  producing 
faradic  currents. 

These  machines  consist  es-  F^' 198' 

sentially  of  a  coil  of  wire  wrapped  on  an  armature  core  rotated 
before  the  poles  of  pei-manent  magnets.  No  commutator  is  em- 
ployed, since  it  is  desired  to  obtain  rapidly  alternating  currents. 


WORDS,  TF.KMS   AND   PHRASES. 


271 


Fui'a«li<-  Brush.— (See  Brush,  Faradic.) 

Faraclic  Current. — In  electro  therapeutics  the  current 
produced  by  an  induction  coil. 

A  rapidly  alternating-  current,  as  distinguished  from  a  uni- 
form voltaic  current. 

A  voltaic  current  that  is  rapidly  alternated  by  means  of 
any  suitable  key  or  switch  is  sometimes  called  a  voltaic  al- 
ti'i'initire.  The  discharge  from  a  Holt?:  machine  is  sometimes 
called  a  Franklinic  Current. 

Faraclic  Induction  Apparatus.— An  induction  coil 
apparatus  for  producing-  farad ic  currents. 

A  voltaic  battery  is  connected  with  the  primary  of  an  induc- 
tion coil,  and  its  cur- 
rent rapidly  broken 
by  an  automatic 
break,  or  by  a  hand 
break.  The  alter- 
nating or  faradic 
currents  thus  pro- 
duced in  the  second- 
ary coils  are  used 
for  electro  therapeu- 
tic purposes.  (See 
Induction  Coil.) 

Faradic  induction 
apparatus  are  made 
in  a  great  variety  of 

forms.    They  all  operate,  however,  on  essentially  the  same 
principles. 

Faradic  machines.— Machines  for  producing  Faradic 
currents. 

These  are  of  two  varieties,  viz. :  magneto-far  ad  ic  apparatus, 
and  simple  induction  apparatus. 

Faradization.— In  electro  therapeutics,  the  effects  pro- 


373  A  DICTIONARY  OP  ELECTRICAL 

duced  on  the  nerves  or  muscles  by  the  use  of  a  faradic  cur- 
i-ent,  in  order  to  distinguish  such  effects  from  galvanization 
or  those  produced  by  a  voltaic  current. 

Fahrenheit's  Thermometer  Scale.— A  thermometer 
scale  in  which  the  length  of  the  thermometer  tube  between 
the  melting1  point  of  ice  and  the  boiling  point  of  water  is 
divided  into  180  equal  parts  called  degrees. 

On  Fahrenheit's  scale,  water  freezes  at  32°  F.  and  boils  at 
212°  F.  Degrees  of  this  thermo-metric  scale  are  represented 
by  an  F.  (See  Centigrade  Thermometer  Scale.) 

False  Pole,  magnetic A  term  proposed  by 

Mascart  and  Joubert,  to  designate  the  extra  magnetic  poles  of 
the  earth,  or  places  acting  as  magnetic  poles,  in  addition  to 
the  two  poles  near  the  earth's  geographical  poles. 

According  to  these  authorities,  the  earth  possesses  two 
magnetic  poles  only,  viz.,  a  negative  pole  in  the  Northern 
Hemisphere,  and  &  positive  pole  in  the  Southern  Hemisphere. 
The  additional  poles,  are  called  by  them  the  false  magnetic 
poles. 

Faults. — Accidential  leaks  in  a  circuit  caused  by  ground 
contacts  or  crosses.     (See  Cross  Contacts.) 
Faults  are  of  three  kinds,  viz.  : 

(1)  Disconnections.     (See  Disconnections.) 

(2)  Earths.    (See  Earths.) 

(3)  Contacts.    (See  Contacts.) 

Various  methods  are  employed  for  detecting  and  localizing 
faults,  for  the  explanation  of  which  reference  should  be  had 
to  standard  electrical  works. 

Faults,  Localization  of (See  Localization  of 

Faults.) 

Ferro-Magiietic  Substances.— A  term  proposed  in 
place  of  paramagnetic,  for  substances  that  are  magnetic, 
after  the  manner  of  iron.  (See  Paramagnetic.) 


WORDS,  TERMS  AND  PHRASES. 


273 


Paramagnetic  is  the  preferable  term.  The  use  of  the 
term  ferromagnetic ia  both  unnecessary  and  unwarranted. 

Fibre-Suspension.— The  suspension  of  a  needle  by 
means  of  a  fibre. 

Fibre  suspension  may  be  effected  by  means  of  a  single 
fibre  or  thread,  or  by  two  parallel  threads,  which  is  called 
bi-filctr  suspension.  (See  Suspension,  Fibre.  Suspension,  Bi- 
filar.} 


Fibre,  Yuleaiiized  - 
Field,  EleetroMtutie 

influence  surround- 
i  ng  a  chai'ged  body. 
Electrostatic  at- 
tractions or  repul- 
sions take  place 
along  certain  lines 
called  lines  of  elec- 
tro static  force. 
These  lines  of  force 
produce  a  field 
called  an  electro- 
static field.  Elec- 
tric level  or  poten- 
tial is  measured 
along  these  lines, 
just  as  gravitation 


— (See  Vulcanized  Fibre.) 
The  region  of  electrostatic 


fig.SOO. 

levels  are  measured  with  a  plumb  line  along  the  lines  of  grav- 
itation force.     (See  Potential.) 

Work  is  done  when  a  body  is  moved  along  the  lines  of  elec- 
trostatic force  in  a  direction  from  an  oppositely  charged  body, 
or  towards  a  similarly  charged  body,  just  as  work  is  done 
against  gravity,  when  a  body  is  moved  along  the  lines  of 
gravitation  force,  away  from  the  earth's  centre,  or  vertically 
upwards. 


274 


A  DICTIONARY  OF  ELECTRICAL 


Field,  Intensity  of (See  Field,  Magnetic.  Field, 

Electrostatic.     Field,  Electro  Magnetic.) 

Field,  Mugiictie The  region  of  magnetic  influ- 
ence surrounding-  the  poles  of  a  magnet. 

Strictly  speaking  a  magnetic  field  is  a  place  where  a  mag- 
netic needle,  if  free  to  move,  will  take  up  a  definite  posi- 
tion. 

Magnetic  attractions  and  repulsions  are  assumed  to  take 
place  along  certain  lines  called  lines  of  magnetic  force.  Their 

direction  in  any  plane 
of  a  magnetic  field,  may 
be  shown  by  sprinkling 
iron  filings  over  a  sheet 
of  paper  held  in  a  hori- 
zontal position  to  a 
magnet  pole  inclined  to 
the  paper  in  the  desired 
plane  and  then  gently 
tapping  the  paper. 

These  are  sometimes 
called  magnetic  figures. 
The  lines  of  force  thus 
shown  will  appear  from 
an  inspection  of  Fig. 200, 
taken  in  a  plane  join 
ing  the  two  poles  of  a 


Fig.  SOI. 


straight  bar  magnet,  and  Fig.  201,  taken  in  a  plane  at  right 
angles  to  the  north  pole  of  a  straight  bar  magnet. 

In  Fig.  200,  the  repulsion  of  the  lines  of  force  at  either  pole 
is  shown  by  the  radiation  of  the  chains  of  magnetized  iron 
particles.  The  mutual  attraction  of  unlike  polarities  is  shown 
by  the  curved  lines. 

In  Fig.  201,  the  repulsion  of  the  similarly  magnetized  chains 
is  clearly  shown. 

Lines  of  magnetic  force  are  assumed  to  pass  out  from  the 


WORDS,  TERMS  AND  PHRASES. 


275 


nortlipole  and  into  the  south  polo.  This  is  called  the  direc- 
tion of  the  linen  of  force. 

The  density  of  a,  iii'ifjnetic  field  is  directly  proportional  to 
the  number  of  linos  of  force  per  uuit  of  area  of  cross  section. 

A  single  line  of  force,  or  a  unit  line  of  force,  is  such  an  in- 
tensity of  field  as  exists  in  each  square  centimetre  of  cross 
section  of  a  unit  magnetic  field. 

A  magnetic  field  is  uniform,  or  possesses  uniform  intensity, 
when  it  possesses  the  saint;  number  of  lines  of  force  per  square 
centimetre  of  area  of  cross  section. 

•  of  an  Electric  Current. — 


Field,  magnetic 

The  magnetic  field 
surroundinga  circuit 
through  which  an 
electric  current  is 
Ho  wing. 

An  electric  current 
produces  a  magnetic 
field.  This  was  dis- 
covered by  Oersted, 
in  1819,  and  may  be 
shown  by  sprinkling 
iron  filings  on  a  sheet 
of  paper,  placed  on 
the  wire  or  conductor 
conveying  the  cur- 
rent, at  right  angles  m^  m- 
to  the  direction  in  which  the  current  is  passing.  Here  the 
lines  of  force  appear  as  concentric  circles,  around  the  con- 
ductor, as  shown  in  Fig.  202.  Their  direction,  as  regards  the 
length  of  the  conductor,  is  shown  in  Fig.  203.  The  electric 
current  sets  up  these  magnetic  whirls  around  the  conductor 
on  its  passage  through  it. 

The  direction  of  the  lines  of  magnetic  force  produced  by  an 
electric  current,  and  hence  its  magnetic  polarity,  depends  on 


276 


A  DICTIONARY  OF  ELECTRICAL 


the  direction  in  which  the  electric  current  flows.  This  direc- 
tion may  be  remembered  as  follows  :  If  the  current  flows  to- 
wards the  observer,  the  direction  of  the  lines 
of  magnetic  force  is  opposite  to  that  of  the  hands 
of  a  watch,  as  shown  in  Fig.  204. 

It  is  from  the  direction  of  the  lines  of  force 
that  the  polarity  of  a  helix  carrying  a  current 
is  deduced.  (See  Magnetic  Solenoid.  Electro- 
Magnet.) 

A  magnetic  field  possesses  the  following  prop- 
erties, viz.  : 

(1)  All  magnetizable  bodies  are  magnetized 
when  brought  into  a  magnetic  field.     (See  In- 
duction, Magnetic.) 

(2)  Conductors  moved    through  a    magnetic 
field  so  as  to  cut  its  lines  of  force,  have  differ- 
ences of  potential  generated  in  them  at  different 
points,  and  if  these  points  be  connected  by  a 
conductor,  an  electric  current  is  produced.     (See 
Induction,  Electro- Magnetic.) 

Figure  of  Merit  of  Galvanometer.— The  reciprocal 
of  the  current  required  to 
produce  a  deflection  of  the 
galvanometer  needle 
through  one  degree  of  the 
scale. 

The  smaller  the  current 
required  to  produce  a  de- 
flection of  one  degree,  the 
greater  the  figure  of  merit, 
or  the  greater  the  sensi- 
tiveness of  the  galvano- 
meter. 

Figures,    Eleetrie Licliteuberg's    Dust 

Figures. — Figures  produced  by  writing  on  a  sheet  of  shellac 


Fig.  203. 


Fig.  20/f. 


WORDS,  TERMS  AND  PHRASES. 


277 


with  a  knob  of  a  Leyden  jar,  and  then  sprinkling  over  it  a 
mixture  of  powdered  sulphur  and  red  lead,  which  have  been 
previously  mixed  together,  and  are  so  rendered,  respectively, 
negative  and  positive. 

The  red  lead  collects  on  the  negative  parts  of  the  shellac 
surface,  and  the  sulphur  on  the  positive  parts,  in  curious 
figures,  known  as  Lichtenberg's  Dust  Figures,  one  of  which  is 
shown  in. Fig.  205. 

These  figures  show  very  clearly  that  an  electric  charge  tends 
to  creep  irregularly  over  the  surface  of  an  insulating  substance 


or  Breath  Figures.— 


Figure*,  Eleetric 

Faint  figures  of 
condensed  vapor 
produced  by  elec- 
trifying a  coin, 
placing  it  mo- 
mentarily on  the 
surface  of  a  sheet 
of  clean,  dry 
glass,  and  then 
breathing  gently 
on  the  spot  where 
the  coin  was 
placed. 

The  moisture 
collects  on  the 
electrified  p  o  r  - 
tions  and  forms  a  fairly  distinct  image  of  the  coin. 

Figures,  IHaguelie  —  — A  name  sometimes  ap- 

plied to  the  groupings  of  iron  filings  on  a  sheet  of  paper  held  in 
a  magnetic  field.    (See  Field,  Magnetic.) 

Filament.— A  slender  thread  or  fibre. 

The  term  is  applied  generally  to  threads  or  fibres  varying 
considerably  in  diameter. 


278  A   DICTIONARY   OF  ELECTRICAL 

Filament  of  Incandescent  Electric  Lamp.— A  term 
now  generally  applied  to  the  incandescing1  conductor  of  an 
incandescent  electric  lamp,  whether  the  same  be  of  very  small 
cross  section,  or  of  comparatively  large  cross  section. 

The  term  filament  is  properly  applied  to  a  conductor  con- 
taining fibres  or  filaments  extending  in  the  general  direction 
of  the  length  of  the  incandescing  conductor.  Such  a  con- 
ductor is  made  of  carbonizable  fibrous  material,  cut  or  shaped 
prior  to  carbonization,  so  as  to  have  the  fibres  extending  with 
their  greatest  length  in  the  direction  of  length  of  the  filament. 

Filament,  Magnetic A  chain  or  thread  of 

magnetized  particles. 

This  is  sometimes  called  a  uniform  magnetic  filament. 
•A  bar-magnet  possesses  but  two  free  poles,  which  when 
broken  at  its  neutral  point  or  equator  will  develop  free  poles  at 
the  broken  ends.  This  is  explained  by  considering  the  magnet 
to  be  composed  of  a  number  of  separate  particles,  separately 
magnetized.  A  single  chain  or  filament  of  such  particles  is 
called  a  magnetic  filament.  (See  Neutral  Point  of  a  Magnet. 
Magnetism,  Hughes'  Theory  of.) 

Fire  Alarm,  Electric  —  —A  system  for  telegraph- 

ically sending  an  alarm  of  fire  from  stations  in  different 
portions  of  a  district  to  the  engine  houses.  (See  Alarm,  Elec- 
tric, Fire.) 

Such  alarms  are  automatic  when  the  alarm  is  sounded  by 
the  completion  of  the  circuits  by  means  of  a  thermostat.  (See 
Thermostat.) 

Fire  Extinguisher,  Electric  —  —  A  thermo- 

stat, or  a  mercury  contact,  which  automatically  completes  the 
circuit  and  turns  on  a  water  supply  for  extinguishing  a  fire, 
on  a  certain  predetermined  increase  of  temperature. 

Fishes,  Electric (See  Animal  Electricity.  Eel, 

Electric.) 


WORDS,  TERMS  AND  PHRASES.  21V 

Flashing  of  Carbons,  Process  for  the 

— A  process  for  improving  the  electrical  uniformity  of  the 
carbon  conductors  employed  in  incandescent  lighting,  by  the 
deposition  of  carbon  in  their  pores,  and  over  their  surfaces  at 
those  places  where  the  electric  resistance  is  comparatively 
great. 

The  carbon  conductor  is  placed  in  a  vessel  usually  filled  with 
the  vapor  of  a  hydro-carbon  liquid  called  rhigolene,  or  any  other 
readily  decomposable  hydro-carbon  liquid,  and  gradually 
raised  to  eleotrical  incandescence  by  the  passage  through  it  of 
an  electric  current.  A  decomposition  of  the  hydro-carbon 
vapor  occurs,  the  carbon  resulting  therefrom  being  deposited 
in  and  on  the  conductor.  If  the  current  is  gradually  increased, 
those  parts  of  the  conductor  which  are  first  rendered  incandes- 
cent, that  is  in  those  parts  where  the  resistance  is  the  highest, 
and  practically  those  parts  only,  receive  the  deposits  of  carbon. 
As  the  current  gradually  increases,  other  portions  become 
successively  incandescent  and  receive  a  deposit  of  carbon, 
until  at  last  the  filament  glows  with  a  uniform  brilliancy,  in- 
dicative of  its  electric  homogeneity. 

A  carbon  whose  resistance  varies  considerably  at  different 
parts  could  not  be  successfully  employed  in  an  incandescent 
lamp,  since  if  heated  by  a  current  sufficiently  great  to  render 
the  points  of  comparatively  small  resistance  satisfactorily  in- 
candescent, the  temperature  of  the  points  of  high  resistance 
would  be  such  as  to  lower  the  life  of  the  lamp,  while  if  only 
those  portions  were  safely  heated,  the  lamp  would  not  be 
economical.  The  flashing  process  is  therefore  of  very  great 
value  in  the  manufacture  of  an  incandescent  lamp. 

Flashing  of  Dynamo  Eleetric  Machine.— A  name 
given  to  long,  Hashing  sparks  at  the  commutator,  usually  due 
to  the  short  circuiting  of  the  external  circuit  at  the  commu- 
tator. 

Floating  Battery,  l>e  la  Rive's A  floating 

voltaic  cell,  the  terminals  of  which  are  connected  with  a  coil 


380  A  DICTIONARY   OF  ELECTRICAL 

of  insulated  wire,  employed  to  show  the  attractions  and  re- 
pulsions between  magnets  and  movable  electric  circuits. 

The  cell,  shown  in  Fig.  206,  consists  of  a  voltaic  couple  of 
zinc  and  copper,  the  terminals  of  which  are  connected  to  the 
circular  coil  of  insulated  wire,  as  shown,  and  the  whole  floated 
by  means  of  a  cork,  in  a  vessel  containing  dilute  sulphuric 
acid. 

When  the  current  flows  through  the  coil  in  the  direction 
shown  by  the  arrows,  the  approach  of  the  N-seeking  pole  of  a 
magnet  will  cause  the  cell  to  be  attracted  or  to  move  to- 
wards the  magnet  pole,  since  the  south  face  or  end  of  the  coil 
is  nearer  the  north  pole  of  the  magnet.  If  the  other  end  were 
nearer,  repulsion  would  occur, 
the  cell  turning  around  until 
the  south  face  is  nearer  the 
magnet,  when  attraction  oc- 
curs. 


Flow.— In  hydraulics,  the 
quantity    of    water  or    other 
fluid  which  escapes  from  an 
orifice  in  a  containing  vessel 
Fig.m.  in  a  given  time. 

Flow Direction  of  Current The  direc- 
tion the  current  is  assumed  to  take,  i.  e.,  from  the  positive 
pole  of  the  source  through  the  circuit  to  the  negative  pole  of 
the  source. 

The  electricity  is  assumed  to  come  out  of  the  source  at  its 
positive  pole,  and  to  return  or  flow  back  into  the  source  at  its 
negative  pole.  (See  Current,  Direction  of.) 

Flow  of  LiiiCM  of  Electrostatic  Force.— A  mathe- 
matical conception  in  which  the  phenomena  of  electricity  are 
compared  with  the  similar  phenomena  of  heat. 

In  heat  no  flow  of  heat  occurs  over  isothermal  surfaces,  or 
surfaces  at  the  same  temperature.  Over  different  isothermal 


WORDS,   TERMS  AND  PHRASES.  281 

surfaces  the  flow  will  vary  with  the  power  of  heat  conduc- 
tion. In  electricity  no  flow  occurs  over  equipotential  sur- 
faces. Specific  Inductive  Capacity  corresponds  to  heat  con- 
ductivity, and  the  lines  of  force  to  the  lines  of  heat  conduction. 
(See  Capacity,  Specific  Inductive.} 

Fluorescence.— A  property,  possessed  by  certain  solid  or 
liquid  substances  of  becoming  self  luminous  while  exposed  to 
the  light. 

Canary  glass,  or  glass  colored  yellow  by  oxide  of  uranium, 
and  a  solution  of  sulphate  of  quinine,  possess  fluorescent  prop- 
erties. The  path  of  a  pencil  of  light  brought  to  a  focus  in 
either  of  these  substances  is  rendered  visible,  by  the  particles 
lying  in  this  path  becoming  self  luminous. 

The  path  of  a  beam  of  light,  entering,  the  dusty  air  of  a 
darkened  chamber,  is  visible  from  the  light  being  diffused  or 
scattered  in  all  directions  by  the  floating  dust  particles.  So 
in  a  fluorescent  substance  the  path  of  the  light  is  also  ren- 
dered visible  by  the  particles  which  lie  in  its  path,  throwing 
out  light  in  all  directions.  There  is,  however,  this  difference, 
that  in  the  case  of  the  dust  particles  the  light  which  comes 
directly  from  the  beam  is  reflected,  while  in  the  case  of  the 
fluorescent  body  the  light  is  from  the  particles  themselves, 
which  are  set  into  vibrations  by  the  light  that  is  passing 
through,  and  has  been  absorbed  by  their  mass. 

Fluorescence  is,  therefore,  a  variety  of  phosphorescence. 
(See  Phosphorescence.} 

Flush  Boxes.— A  box  or  space,  flush  with  the  surface  of 
a  road  bed,  provided  in  a  system  of  underground  wires  or 
conduits,  to  facilitate  the  introduction  of  the  conductors  into 
the  conduit,  or  for  the  examination  of  the  conductors. 

Flyer,  Electric Electric  Fly,  or  Electric  Re- 
action Wheel. — A  wheel  arranged  so  as  to  be  set  into  rota- 
tion by  the  escape  of  convection  streams  from  its  points  when 
placed  on  a  charged  conductor. 


A  DICTIONARY  OF   ELECTRICAL 


A  wheel  formed  of  light  radial  arms  P,  P,  shaped  as  shown 
in  Fig.  207,  and  capable  of  rotation  on  the  vertical  axis  A,  is 
set  into  rapid  rotation  when  connected  with  the  prime  conduc- 
tor of  a  machine,  through  the  convection  streams  of  air  parti- 
cles which  are  shot  off  from  the  points  or  extremities  of  the 
radial  arm.  The  wheel  is  driven  by  the  reaction  of  these 
streams  in  a  direction  opposite  to  that  of  their  escape.  (See 
Discharge,  Convective.) 

Focus. — The  point  in  front  or  back  of  a  lens,  or  mirror, 
where  the  rays  of  light  meet.      (See 
Achromatic  Lens.) 
Fog,  Electric Dense  fogs 


which  occur  on  rare  occasions  when 
there  is  an  unusual  quantity  of  free 
electricity  in  the  atmosphere. 

During  these  electric  fogs  the  free 
electricity  of  the  atmosphere  changes 
its  polarity  at  frequent  intervals. 

Following  Horn*  of  I>yiiamo- 
Elcctric  Machine.  —  (See  Horns, 
F  allowing ,  of  Dynamo-Electric 
Machine.) 

Foot  Candle.— (See  Candle,  Foot.) 
Foot-I'oimd.— A  unit  of  work.     (See  Work.) 
The  amount  of  work  required  to  raise  one  pound  vertically 
through  a  distance  of  one  foot. 

The  same  amonnt  of  work  is  done  by  raising  one  pound 
through  a  vertical  distance  of  three  feet,  or  three  pounds 
through  a  vertical  distance  of  one  foot,  viz.,  three  foot- 
pounds. 

Apart  from  air  friction,  the  amount  of  work  done  in  raising 
one  pound  through  one  foot,  viz.,  one  foot-pound,  is  the  same 
whether  this  work  be  done  in  one  second,  or  in  one  day.  The 
poiver,  however,  or  the  rate  of  doing  ivork  is  very  different  in 
the  two  cases.  (See  Poiver.) 


AVORDS,  TERMS  AND  PHRASES.  283 

For  another  unit  of  work,  see  the  Erg. 

Force.— Any  cause  which  changes  the  condition  of  rest  or 
motion  of  a  body. 

Force,  Centrifugal  —       •  —(See  Centrifugal  Force.) 

Force,  Coercive  or  Cocrcitive or  Magnetic 

Retentivity.— The  power  of  resisting  magnetization  or  de- 
magnitization.  (See  Coercive  Force.) 

Force,  Composition  of (See  Components.) 

Force,  Electrostatic The  force  producing  the 

attractions  or  repulsions  of  charged  bodies. 

Force,  Lines  of  Electrostatic (Sec  Field, 

Electro-Static.) 

Force,  Lines  of  magnetic (See  Field,  Mag- 
netic.) 

Force,  Magnetic The  force  which  causes  the  at- 
tractions or  repulsions  of  magnet  poles.  (See  Magnetic  Force.) 

Force,  Resolution  of (See  Resultants.) 

Force,  Tubes  of or  Tubes  of  Induction.— 

Tubes  bounded  by  lines  of  electrostatic  or  magnetic  force. 

Lines  of  force  never  intersect  one  another.  Hence  a  tube  of 
force  may  be  regarded  as  containing  the  same  number  of  lines 
of  force  at  any  and  every  cross  section. 

Tubes  of  electrostatic  force  always  terminate  against  equal 
quantities  of  positive  and  negative  electricity  respectively. 
They  terminate  when  they  meet  a  conducting  surface. 

The  term  tubes  of  force  is  somewhat  misleading,  since  such 
so-called  tubes  are  in  general  cones  rather  than  tubes. 

Force,  Unit  of or  I>yiie.— A  force,  which  acting 

for  one  second,  on  a  mass  of  one  gramme,  will  give  it  a  ve- 
locity of  one  centimetre  per  second.  (See  Dyw.) 

Forces,  Parallelogram  of A  parallelogram 

constructed  about  the  two  lines  that  represent  the  direction 
and  intensity  with  which  two  forces  are  simultaaxwusly  acting 


384  A  DICTIONARY  OF  ELECTRICAL 

on  a  body,  in  order  to  determine  the  direction  and  intensity 
of  the  resultant  force  with  which  it  moves. 

If  the  two  forces  A  C  and  A  B,  Fig.  208,  simultaneously 
act  in  the  direction  of  the  arrows  on  a  body  at  A,  the  direction 
and  intensity  of  the  resultant,  A  D,  is  determined  by  draw- 
ing D  C  and  B  D,  parallel  respectively  to  A  B,  and  A  C. 
The  diagonal  A  D,  of  the  parallelogram  A  C  D  B,  thus  pro- 
duced, gives  this  resultant.  (See  Components.) 

Forming  Plates  of  Secondary  or  Storage  Cells.— 

Obtaining  a  thick  coating  of  lead  monoxide  on  the  plates  of 
a  storage  cell, 'by  repeatedly  sending  the  charging  current 
through  the  cell  alternately  in  opposite  directions.  (See 
Storage  of  Electricity.) 

\D  >,      ForniuhE.— Mathematical  expressions 
Br-  3fr—  for  Some  general  rule  or  principle. 

Formulae    are   of    great    assistance    in 

j        science  in  expressing  the  relations  which 

A  exist  between  certain  forces  or    values, 

Fig.  208.  amj  ^e  effec^s  that  result  from  their  oper- 

ation, since  they  enable  us  to  express  these  relations  in  clear 
and  concise  forms. 

Thus,  in  the  formulation  of  Ohm's  law, 

E 
C  =  —  , 

R 

we  see  that  the  current  C,  in  any  circuit  is  equal  to  the  elec- 
tro-motive force  E,  divided  by  the  resistance  R.  Again,  we 
see  that  the  current  is  directly  proportional  to  the  electro- 
motive force,  and  inversely  proportional  to  the  resistance. 

Formula}  are  usually  written  in  the  form  of  an  equation, 
and  therefore  contain  the  sign  of  equality  or  —. 

Formulae,    Photometrie    —(See   Photometric 

Formulae.) 

Foiieault  Currents,  Eddy  Currents,  Parasitical 
Currents,  Local  Action.— (See  Currents,  Eddy.) 


WORDS,  TERMS  AND  PHRASES.  285 

Frankliiiic  Electricity.— A  term,  sometimes  employed 
in  electro  therapeutics,  for  the  electricity  produced  by  a  fric- 
tional  or  an  electrostatic  induction  machine. 

Free  Charge,  Free  Electricity.— (See  Charge,  Bound 
anil  Free.) 

Frictioiial  Electricity.— Electricity  produced  by  fric- 
tion. 

This  term  as  formerly  employed  to  indicate  static  charges 
as  distinguished  from  currents,  is  gradually  falling  into  dis- 
use, and  the  frictional  electric 
machines,  are  being  generally 
replaced  by  continuous  induc- 
tion machines,  like  those  of 
Holtz,  Tupler-Holtz,  orWims- 
liurst. 

Frog,  Galvaiioscopic  . 

The  hind  legs  of  a  re- 


cently killed  frog,  employed 
as  an  electroscope  or  galvano- 
scope  by  sending  an  electric 
current  from  the  nerves  to 
the  muscles.  (See  Electro- 
scope. ) 

In  1786,  Luigi  Galvani,  made 

the  observation  that  when  the  Fi^  s09- 

legs  of  a  recently  killed  frog  were  touched  by  a  metallic  con- 
ductor connecting  the  nerves  with  the  muscles,  the  legs  were 
convulsed  as  though  alive.  He  repeated  this  experiment, 
and  found  the  movements  were  more  pronounced  when  two 
dissimilar  metals,  such  as  iron  and  copper,  were  employed  in 
the  manner  shown  in  Fig.  209. 

Tills  classic  experiment  created  intense  excitement  in  the 
scientific  world,  and  (Jalvani  at  first  believed  that  he  had  dis- 
covered the  true  vital  fluid  of  the  animal,  but  afterwards 


286  A   DICTIONARY  OP  ELECTRICAL 

recognized  it  as  electricity,  which  he  helieved  to  be  obtained 
from  the  body  of  the  animal.  Volta,  claimed  that  the  move- 
ments were  due  to  electricity  caused  by  the  contact  of  dissi- 
milar metals,  and  thus  produced  his  famous  violtaie  pile.  (See 
Pile,  Voltaic.) 

Fulgurite. — A  tube  of  vitrified  sand,  believed  to  be  formed 
by  a  bolt  of  lightning. 

The  fulgurite  consists  of  an  irregular  shaped  tube  of  glass 
formed  of  sand  which  has  been  melted  by  the  electric  dis- 
charge. 

Fulminate* — The  name  of  a  class  of  highly  explosive 
compounds. 

Fulminating  gold,  silver,  and  mercury,  are  highly  explos- 
ive substances.  Fulminates  are  employed  on  percussion  caps. 

Functions,  Trigonometric (See  Trigonomet- 
ric Functions.} 
Fundamental  Units.— (See  Units,  Fundamental.) 

Furnace,  Electric A  furnace  in  which  heat, 

genei'ated  electrically,  is  employed  for  the  purpose  of  effect- 
ing- difficult  fusions,  for  the  extraction  of  metals  from  their 
ores,  or  for  other  metallurgical  operations. 

In  electric  furnaces  the  heat  is  derived  either  from  electric 
incandescence,  or  from  the  voltaic  arc.  The  latter  form  is 
frequently  adopted. 

The  substance  to  be  treated  is  exposed  directly  to  the  vol- 
taic arc.  In  some  forms  of  furnace  the  crushed  ore  is  per- 
mitted to  fall  through  the  arc,  and  the  melted  matter  received 
in  a  suitable  vessel,  in  which  the  separation  of  the  substances 
so  formed,  is  afterwards  completed.  In  other  forms  of  furnace, 
the  ore  is  placed  between  two  electrodes  of  carbon  or  other 
refractory  substances,  between  which  a  powerful  current  is 
passed.  In  the  Cowles  furnace,  when  aluminium  is  reduced, 
molten  copper  forms  an  alloy  with  the  aluminium  as  soon  as 
it  is  sepai*ated. 


WORDS,  TERMS  AND  PHRASES.  287 

Very  numerous  applications  of  electricity  to  furnace  opera- 
tions have  been  inaile,  for  details  of  which,  standard  works 
should  be  consulted. 

Fuse,  Electric A  device  for  electrically  igniting 

a  charge  of  powder. 

Electric  fuses  are  employed  both  in  blasting  operations  and 
for  firing  cannon. 

Electric  fuses  are  operated  either  by  means  of  the  direct 
spark,   or  by  the  incandescence  of  a  thin  wire, 
placed  in  the  circuit.     They  are  therefore  either 
high  tension,  or  Icnv  tension  fuses. 

The  advantages  of  an  electric  fuse  consist  in  the 
fact  that  its  use  permits  the  simultaneous  firing 
of  a  number  of  charges  in  a  mining  operation,  thus 
obtaining  a  greater  effect  from  the  explosion.  A 
fulminate  of  mercury  is  frequently  employed  in 
connection  with  some  forms  of  electric  fuses. 

A  form  of  fuse  in  which  the  ignition  is  effected 
by  the  electric  spark  is  shown  in  Fig.  210,  and  is 
known  as  Stratham's  fuse.  The  spark  passes 
through  a  break  A  B,  in  the  insulated  leads  D. 
Since  gunpowder  is  not  readily  ignited  by  an 
electric  spark,  a  peculiar  priming  material  is  em- 
ployed at  A  B,  in  the  place  of  ordinary  powder. 

Fuse,  Safety Safety  Strip,  or  Safety 

Plug.— A  strip,  plate,  or  bar  of  lead  or  some 

readily  fusible  alloy,  that  automatically  breaks 

the  circuit  in  which  it  is  placed  on  the  passage  of  a  current 

of  sufficient  power  to  fuse  such  strip,  plate,  or  bar,  when 

such  current  would  endanger  the  safety  of  other  parts  of 

the  circuit. 

SalVty  fuses  are  made  of  alloys  of  lead,  and  are  placed  in 
boxes,  lined  with  non-combustible  material,  in  order  to  pre- 
vent fires  from  the  molten  metal.  Fig.  211,  shows  a  fusible 
strip  F,  connected  with  leads  L,  L.  Safety  fuses  are  placed 


A  DICTIONARY  OP  ELECTRICAL 


on  all  branch  circuits,  and  are  made  of  sizes  proportionate  to 
the  number  of  lamps  they  guard. 

Since  incandescent  lamps  are  generally  connected  with  the 
circuit  in  multiple-arc,  or  in  multiple-series,  one  or  more  of 
the  circuits  can  be  opened  by  the  fusion  of  the  plug  with- 
out interfering  with  the  continuity  of  the  rest  of  the  circuit. 
In  series  circuits,  however,  such  as  arc  light  circuits,  when  a 
lamp  is  cut  out,  a  short  circuit  or  path  around  it  must  be  pro- 
vided to  avoid  the  extinguishing  of  the  rest  of  the  lights. 


Fig.  211. 

Galvanic  Battery— Two  or  more  voltaic  cells  so  ar- 
ranged as  to  form  a  single  source.  (See  Battery,  Voltaic.) 

Galvanic  Cell.— (See  Cell,  Voltaic.) 
Galvanic  Circle.— (See  Circle,  Galvanic.) 

Galvanic  Circuit. — A  term  sometimes  employed  instead 
of  the  term  voltaic  circuit.  The  term  galvanic  in  place  of 
voltaic  is  unwarranted  by  the  facts  of  electric  science.  ( See 
Circuit,  Voltaic.) 

Galvani  thought  he  had  discovered  the  vital  fluid  of  animals . 
Volta  first  pointed  out  the  true  explanation  of  the  phenomena 
observed  inGalvani's  frog,  and  devised  the  means  for  produc- 
ing electricity  in  this  manner.  The  terms  voltaic  battery,  cell, 
circuit,  etc.,  are  therefore  preferable. 


WORDS,  TERMS  AND  PHRASED.  286 

Galvanic  Polarization.— A  term  sometimes  applied  to 
the  polarization  of  a  voltaic  cell.  (See  Polarization  of  Vol- 
taic Cell.) 

Galvanism.— A  term  sometimes  employed  to  express  the 
effects  produced  by  voltaic  electricity. 

Galvanization.— In  electro  therapeutics  the  effects  pro- 
duced on  nervous  or  muscular  tissue  by  the  passage  of  a 
voltaic  current. 

In  electro-metallurgy,  the  process  of  covering  any  con- 
ducting surface  with  a  metallic  coating  by  electrolytic  de- 
position, such,  for  example,  as  the  thin  copper  coating 
deposited  on  the  carbon  pencils  or  electrodes  used  in  systems 
of  arc  lighting. 

This  term  is  borrowed  from  the  French,  in  which  it  has  the 
above  signification.  It  is  preferably  replaced  by  the  term 
electro-plating.  (See  Electro-Plating.) 

It  is  never  correctly  applied  to  the  process  for  covering  iron 
with  zinc  or  other  metal  by  dipping  the  same  in  a  bath  of 
molten  metal. 

Galvanized  Iron.— Iron  covered  with  a  layer  of  zinc  by 
dipping  in  a  bath  of  molten  zinc. 

The  process  of  galvanizing  iron  is  designed  to  prevent  the 
corrosion  or  rusting  of  the  iron  on  exposure  to  the  air.  (See 
Metals,  Electrical  Protection  of.) 

Galvaiio-Cautery.— (See  Cautery,  Electric.) 

Galvaiio-Faradization.—  In  electro  therapeutics  the 
simultaneous  excitation  of  a  nerve  or  muscle  by  both  a  voltaic 
and  afaradic  current. 

Galvanometer.— An  apparatus  for  measuring  the 
strength  of  an  electric  current  by  the  deflection  of  a  magnetic 
needle. 

The  galvanometer  depends  for  its  operation  on  the  fact 
that  a  conductor,  through  which  an  electric  current  is  flowing, 


A  DICTIONARY  OF  ELECTRICAL 


will  deflect  a  magnetic  needle  placed  near  it.  This  deflection 
is  due  to  the  magnetic  field  caused  by  the  current.  (See 
Field,  Magnetic,  of  Current.) 

This  action  of  the  current 
was  first  discovered  by  Oer- 
sted. A  wire  conveying  a 
current  in  the  direction  shown 
by  the  straight  arrow,  Fig. 
212,  or  from  -f-  to  — ,  will 
deflect  a  magnetic  needle  in 
the  direction  shown  by  the 
curved  arrows. 


Fig.  212. 


If  the  wire  be  bent  in  the 


form  of  a  hollow  rectangle  F  D  E  G,  Fig.  213,  and  the  needle, 

M,  be  placed  inside  the  circuit,  the  upper  and  lower  branches  of 

the  current,  Avill  deflect 

the  needle  in  the  same 

direction,  and  the  effect 

of  the  current  will  thus 

be  multiplied.   Mercury 

cups  are  provided  at  A, 

B  and  C,   for  a  ready 

change  in  the  direction 

of   the    circuit.      (See 

Astatic  Needle.) 

This  principle  of  the 
multiplication  of  the 
deflecting  power  of  the 
current  was  applied  to 
galvanometers  by  Fig. sis. 

Schweigger,  who  used  a  number  of  turns  of  insulated  wire  for 
the  greater  deflection  of  the  needle.  He  called  such  a  device 
a  multiplier.  In  extremely  sensitive  galvanometers  very 
many  turns  of  wire  are  employed,  in  some  cases  amounting 
to  many  thousands.  Such  galvanometers  are  of  a  high  resist- 


WORDS,  TERMS  AND  PHRASES.  291 

ance.  Others,  of  low  resistance,  often  consist  of  a  single  turn  of 
wire  and  are  used  in  the  direct  measurement  of  large  currents. 

A  Schweigger's  multiplier  or  coil  C  C,  of  many  turns  of 
insulated  wire,  is  shown  in  Fig.  214.  The  action  of  such  a 
coil,  on  the  needle  M,  is  comparatively  great,  even  when  the 
current  is  small. 

In  the  case  of  any  galvanometer,  the  needle  when  at  rest, 
and  no  current  is  passing,  should  in  general,  occupy  a  posi- 
tion parallel  to  the  length  of  the  coil.  On  the  passage  of  the 
c  u  r  rent  the 
needle  tends  to 
place  itself  in  a 
position  at  right 
angles  to  the  di- 
rection of  the  cur- 
rent, or  to  the 
length  of  the  con- 
ducting wire  in 
the  coil.  The 
strength  of  the 
current  passing  is  Fig.  nit. 

determined  by  observing  the  amount  of  this  deflection  as 
measured  in  degrees  on  a  graduated  circle  over  which  the 
needle  moves. 

The  needle  is  deflected  by  the  current  from  a  position  of 
rest,  either  in  the  earth's  magnetic  field,  or  in  a  field  obtained 
from  a  permanent,  or  an  electro  magnet.  In  the  first  case, 
when  in  use  to  measure  a  current,  the  plane  of  the  galvano- 
meter coils  must  coincide  with  the  plane  of  the  magnetic  meri- 
dian. In  the  other  case,  the  instrument  may  be  used  in  any 
position  in  which  the  needle  is  free  to  move. 

Galvanometers  assume  a  variety  of  forms  according  either 
to  the  purposes  for  which  they  are  employed,  or  to  the  manner 
in  which  their  deflections  are  valued. 

Galvanometer,    Absolute A    galvanometer 

With  an  absolute  calibration.    (See  Calibration,  Absolute.) 


A  DICTIONARY  OF  ELECTRICAL 


Such  a  galvanometer  is  called  absolute  because  if  the  dimen- 
sions of  its  coil  and  needle  are  known,  the  current  can  be  de- 
termined directly  from  the  observed  deflection  of  the  needle. 

Galvanometer,  A  periodic (See  Galvanometer, 

Dead  Beat.) 


Galvanometer,  Astatic 


— A  galvanome- 


ter, the  needle  of  which  is  astatic.     (See  Astatic  Needle.) 

Nobili's  astatic  galvanometer  is  shown  in  Fig.  215.  The 
astatic  needle,  suspended  by  a  fibre  6,  has  its  lower  needle 
placed  inside  a  cpil  a,  consisting  of  many  turns  of  insulated 
wire,  its  upper  needle  moving  over 
the  graduated  dial.  The  current 
to  be  measured  is  led  into  and  from 
the  coil  at  the  binding  posts  x 
and  y. 

In  this  instrument,  if  small  de- 
flections only  are  employed,  the 
deflections  are  sensibly  proportion- 
al to  the  strength  of  the  deflecting 
currents. 

Galvanometer,  B  a  1 1  i  s  1 1  c 

A   galvanometer 


Fig.  315.  designed  to  measure  the  strength 

of  currents  that  last  but  for  a  moment,  such  for  example,  as 
the  current  caused  by  the  discharge  of  a  condenser. 

The  quantity  of  electricity  passing  in  any  circuit  is  equal 
to  the  product  of  the  current  and  the  time  Since  the  cur- 
rent caused  by  the  discharge  of  a  condenser  lasts  but  for  a 
small  time,  during  which  it  passes  rapidly  from  zero  to  a 
maximum  and  back  again  to  zero,  the  magnetic  needle  in  a 
ballistic  galvanometer  takes  the  form  of  a  ballistic  pendulum, 
i.  e.,  it  is  given  such  a  mass,  and  acquires  such  a  slow  mo- 
tion, that  its  change  of  position  does  not  practically  begin 
until  the  impulses  have  ceased  to  act. 


WORDS,  TEEMS  AND  PHRASES. 


293 


In  the  ballistic  galvanometer  of  Siemens  and  Halske,  the 
coils  K,  R,  Fig.  21G,  have  a  bell-shaped  magnet  M,  suspended 


Fig.  sie. 
inside  them  by  means  of  an  aluminium  wire.     The  magnet 


394 


A  DICTIONARY  OF  ELECTRICAL 


provided  with  a  mirror  S,  for  measuring  the  deflections.  The 
bell-shaped  magnet  is  shown  in  elevation  at  M,  and  in  plan 
at  n,  s. 

In  using  the  ballistic  galvanometer  it  is  necessary  to  see 
that  the  needle  is  absolutely  at  rest  before  the  discharge  is 
sent  through  the  coils. 

Galvanometer,  Dead  Beat A  galvanometer, 

the  needle  of  which 
comes  quickly  to  rest, 
instead  of  swinging  re- 
peatedly to  and  fro. 
(See  Damping.) 
Oalvaiio  meter, 

Differential 

A  galvanometer  con- 
taining two  coils  so 
wound  as  to  tend  to  de- 
flect the  needle  in  op- 
posite directions. 

The  needle  of  a  differ- 
e  n  t  i  a  1  galvanometer 
shows    no  deflection 
when   two    equal    cur- 
rents are  sent  through 
the    coils    in    opposite 
directions,  since,  under 
these    conditions    each 
coil  neutralizes  the 
other's    effects.      Such 
instruments    may   be 
used  in  comparing  re- 
sistances.   The  Wheatstone  Bridge,  however,  in  most  cases, 
affords  a  preferable  method  for  such  purposes.     (See  Balance, 
Wheatstone's.) 
A  form  of  differential  galvanometer  is  shown  in  Fig.  217. 


WORDS,  TERMS  AND  PHRASES. 


295 


Sometimes  the  current  is  sent  through  the  two  coils  so  that 
each  coil  deflects  the  needle  in  the  same  direction.  In  this 
case,  the  instrument  is  no  longer  differential  in  action.  If 
the  magnetic  needle,  in  such  cases,  is  suspended  at  the  exact 
centre  of  the  line  which  joins  the  centres  of  the  coils,  the 
advantage  is  gained  of  obtaining  a  field  of  more  nearly  uni; 
form  intensity  around  the  needle. 

Galvanometer,  Figure  of  Merit  of  - 
—  (See  Figure  of  Merit  of  Galvanometer.) 

Galvanometer,  Marine  ---  A  galvanometer 
devised  by  Sir  Wm.  Thomson  for  use  on  steamships  where 
the  motion  of  magnetized  masses  of  iron  would  seriously  dis- 
turb the  needles  of  ordinary  instruments. 


Fig.  218. 

The  needle  of  the  marine  galvanometer  is  shielded  or  cut 
off  from  the  extraneous  fields  so  produced,  by  the  use  of  a 
magnetic  screen  or  shield,  consisting  of  an  iron  box  with  thick 
sides,  inside  of  ichich  the  instrument  is  placed. 

The  needle  is  suspended  by  means  of  a  silk  fibre  attached 
both  above  and  below,  and  passing  through  the  centre  of 
gravity  of  the  needle.  In  this  manner  the  oscillations  of  the 
ship  do  not  affect  the  needle. 


296 


A  DICTIONARY  OF  ELECTRICAL 


Galvanometer,  Mirror A  galvanometer  in 

which,  instead  of  reading  the  deflections  of  the  needle  directly 
by  its  movement  over  a  graduated  circle,  they  are  read  by  the 
movements  of  a  spot  of  light  reflected  from  a  mirror  attached 
to  the  needle. 

This  spot  of  light  moves  over  a  graduated  scale,  or  its 
movements  are  observed  by  means  of  a  telescope. 

A  form  of  mirror  galvanometer  designed  by  Sir  Wm. 
Thomson,  is  shown  iu  Fig.  218.  The  needle  is  attached 
directly  to  the  back  of  a  light,  sil- 
vered glass  mirror,  and  consists  of 
several  small  magnets  made  of  pieces 
of  a  watch  spring.  The  needle  and  mir- 
ror are  suspended  by  a  single  silk  fibre 
and  are  placed  inside  the  coil.  A  com- 
pensating magnet  N  S,  movable  on  a 
vertical  axis,  is  used  to  vary  the  sen- 
sitiveness of  the  instrument.  The  lamp 
L,  placed  back  of  a  slot  in  a  wide 
screen,  throws  a  pencil  of  light  on  the 
mirror  Q,  from  which  it  is  reflected  to 
the  scale  K. 

Galvanometer  Shunt.— A  shunt 
fig.  219.  placed  around  a  sensitive  galvanometer 

for  the  purpose  of  protecting  it  from  the  effects  of  a  strong 
current,  or  for  altering  its  sensibility.  (See  Shunt.) 

The  cm-rent  which  will  flow  through  the  shunt  wire  depends 
on  the  relative  resistance  of  the  galvanometer  and  of  the  shunt. 
In  order  that  only  -fa,  ^  or  T5Vff  of  the  total  current  shall 
pass  through  the  galvanometer,  it  is  necessary  that  the  re- 
sistances of  the  shunt  shall  be  the  J,  ,V  or  ¥J5  of  the  galvanome- 
ter resistance. 

Fig.  219,  shows  a  shunt,  in  which  the  resistances,  as  com- 
pared with  that  of  the  galvanometer  are  those  above  referred 
to.  The  galvanometer  terminals  are  connected  at  N  N.  Plug 


WORDS,  TERMS  AND  PHRASES. 


297 


keys  are  used  to  connect  one  or  another  of  the  shunts  into 
the  circuit.     (See  Multiplying  Power  of  Shunt.) 


Galvanometer,  Sine 


— A  galvanometer  in  which 


a  vertical  coil  is  movable  around  a  vertical  axis,  so  that  it  can 
be  made  to  follow  the  magnetic  needle  in  its  deflections. 


Fig.  220. 

In  the  sine  galvanometer  the  coil  is  moved  so  as  to  follow 
the  needle,  until  it  is  parallel  with  the  coil.  Under  these  cir- 
cumstances the  strength  of  the  deflecting  currents  in  any  two 
different  cases  is  proportional  to  the  sine  of  the  angle  of  de- 
flection. 


A  DICTIONARY  OF  ELECTRICAL 


A  form  of  sine  galvanometer  is  shown  in  Fig.  220.  The 
vertical  wire  coil  is  seen  at  M.  A  needle,  of  any  length  less 
than  the  diameter  of  the  coil  M,  moves  over  the  graduated 
circle  N.  The  coil  M,  is  movable  over  the  graduated  horizontal 
circle  H,  by  which  the  amount  of  the  movement  necessary  to 
bring  the  needle  to  zero  is  measured.  The  current  strength  is 
proportional  to  the  sine  of  the  angle  measured  on  this  circle, 
through  which  it  is  necessary  to  move  the  coil  M  from  its 
position  when  the  needle  is  at  rest  in  the  plane  of  the  earth's 
magnetic  meridian,  until  the  needle  is  not  further  deflected  by 
the  current,  although  parallel  to  the  coil  M. 

Galvanometer,    Tangent An  instrument    in 

which  the  deflecting  coil  consists 
of  a  coil  of  wire  within  which  is 
placed  a  needle  very  short  in  pro- 
portion to  the  diameter  of  the  coil, 
and  supported  at  the  centre  of  the 
coil. 

A  galvanometer  acts  as  a  tan- 
gent galvanometer  only  when  the 
needle  is  very  small  as  compared 
with  the  diameter  of  the  coil.  The 
length  of  the  needle  should  be  less 
than  one-twelfth  the  diameter  of 
the  coil. 

fig.  Ml.  A  form  of  tangent  galvanometer 

is  shown  in  Fig.   221.     The  needle  is  supported  at  the  exact 
centre  of  the  coil  C. 

Under  these  circumstances  the  strengths  of  two  different  de- 
flecting currents  are  proportional  to  the  tangents  of  the  angles 
of  deflection.  Tangent  galvanometers  are  sometimes  made 
with  coils  of  wire  containing  many  separate  turns. 

Galvanometer,  Tangent, Obaeli's. — A  form 

of  galvanometer  in  which  the  deflecting  coil,  instead  of  being 
in  a  fixed  vertical   position,   is   movable  about  a  horizontal 


WORDS,  TERMS  AND  PHRASES. 


axis,  so  as  to  decrease  the  delicacy  of  the  instrument,  and  thus 
increase  its  range  of  work. 

Galvanometer,  Torsion A  galvanometer  in 

which  the  strength  of  the  deflecting  current  is  measured  by 
the  torsion  exerted  on  the  suspension  system. 

A  bell-shaped  magnet,  shown  at  the  right  of  Fig.  222,  is 
suspended  by  a  thread  and  a  spiral  spring  between  two 
coils  of  high  resistance,  placed  parallel  to  each  other  in  the 
positions  shown.  On 
the  deflection  of  the 
magnet,  by  the  cur- 
rent to  be  measured, 
the  strength  of  the 
current  is  determined 
by  the  amount  of  the 
torsion  required  to 
bring  the  magnet 
back  to  its  zero  point. 
The  angle  of  torsion 
is  measured  on  the 
horizontal  scale  at  the 
top  of  the  instrument. 

In  the  torsion  gal- 
vanometer, unlike  the 
electro-dynamometer, 
the  action  between  the 
coils  and  the  movable 
magnet  is  as  the  cur- 
rent strength  causing 
the  deflection.  In  the 
electro  dynamometer, 
such  an  increase  in  the  deflecting  coil  produces  a  corresponding 
increase  in  the  deflected  coil ;  the  mutual  action  of  the  two 
is  as  the  square  of  the  current  strength  causing  the  deflection. 

Galvanometer,  Vertical A  galvanometer,  the 

needle  of  which  is  capable  of  motion  in  a  vertical  plane  only. 


300 


A  DICTIONARY  OF  ELECTRICAL 


In  the  vertical  galvanometer  the  north  pole  is  weighted  so 
that  the  needle  assumes  a  vertical  position  when  no  current  is 
passing.  In  the  form  shown,  in  Fig.  223,  two  needles  are  some- 
times employed,  one  of  which  is  placed  inside  the  coils  C,  C. 

The  vertical  galvanometer  is  not  as  sensitive  as  the  ordinary 
forms.  It  is  employed,  however,  in  various  forms  for  an 
electric  current  indicator  or  even  for  a  rough  current 
measurer. 

Galvanometer,  Volt-Meter An    instrument 

devised  by  Sir  Wm.  Thomson,  for  the  measurement  of  differ- 
ences of  electric?  potential. 

This  instrument  is  so  arranged  that  by  a  simple  correction 

for  the  varying 
strength  of  the 
earth's  field  in  any 
place,  the  results  are 
read  at  once  in  volts. 
A  coil  of  insulated 
wire,  shown  at  A, 
Fig.  224,  has  a  resist- 
ance of  over  5,000 
ohms.  A  magnetic 
needle,  formed  of 
short  parallel 
needles  placed  above 
one  another  and 
called  a  magnetome- 
ter needle,is  attached 
to  a  long  but  light 
aluminium  index, 
moving  over  a  grad- 
uated scale.  A  mov- 
able, semi-circular 
magnet  B,  called  the  restoring  magnet,  is  placed  over  the 
needle,  and  is  used  for  varying  the  effect  of  the  earth's  field 


WORDS,  TERMS  AND  PHRASES. 


301 


at  any  point.  The  sensitiveness  of  the  instrument  may  be 
varied  either  by  the  restoring-  magnet,  or  by  sliding  the  mag- 
netometer  boM  nearer  to,  or  further  away  from  the  coil. 

The  volt-meter  galvanometer  depends  for  iis  operation  on  the 
fact  that  when  a  galvanometer  of  sufficiently  high  resistance 
is  introduced  between  any  two  points  in  a  circuit,  the  current 
that  passes  through  it,  and  hence  the  deflection  of  its  needle, 
is  directly  proportional  to  the  difference  of  potential  between 
such  two  points. 

Galvanometers  for  the  commercial  measurement  of  cur- 
rents assume  a  variety  of  forms.  They  are  generally  so  con- 
structed as  to  read  off  the  amperes,  volts,  ohms,  watts,  etc., 
directly.  They  are  called  amperemeters  or  ammeters,  volt- 
meters, ohmmeters,  wattmeters,  etc.  For  their  fuller  descrip- 
tion reference  should  be  had  to  standard  electrical  works. 


Fig. 


Galvano-Plastics.—  A  term  formerly  employed  to  ex- 
press electrotypingor  electro-metallurgical  processes,  but  now 
generally  abandoned.  (See  Electro-Metallurgy.) 

Galvaiio-Puiicture.—  In  electro  therapeutics  the  treat- 
ment of  diseased  parts  of  the  body  by  the  introduction  therein 
of  electrolytic  needles.  (See  Electro-Puncture.} 

Galvaiioscopic  Frog.—  (See  Frog,  Galvanoscopic.) 

Gas-Battery.—  A  battery  in  which  the  elements  consumed 
are  gases  as  distinguished  from  solids. 


803 


A  DICTIONARY  OP  ELECTRICAL 


The  electrodes  of  a  gas  battery  generally  consist  of  plates  of 
platinum,  or  other  solid  substance  which  possesses  the  power 
of  occluding  oxygen  and  hydrogen,  the  lower  parts  of  which 
plates  dip  into  dilute  sulphuric  acid,  and  the  upper  parts  are 
respectively  surrounded  by  oxygen  and  hydrogen  gas  derived 
from  the  electrolytic  decomposition  of  the  dilute  acid. 


A  gas  battery  consisting  of  plates  of  platinum  dipping 
below  into  acid  liquid,  and  surrounded  in  the  space  above  the 
liquid  by  hydrogen  and  oxygen  H,  H'  and  O,  O',  etc.,  respect- 
ively, is  shown  in  Fig.  225. 

In  charging  this  battery  an  electric  current  is  sent  through 
it  until  a  certain  quantity  of  the  gases  has  been  produced. 
If,  then  the  charging  current  be  discontinued,  a  current  in 
the  opposite  direction  is  produced  by  the  battery.  The  gas 
battery  is  in  reality  a  variety  of  storage  battery.  (See  Storage 
of  Electricity.  Storage  Cells.) 

Gas  batteries  can  also  be  made  by  feeding  continually  a  gas 
capable  of  acting  on  the  positive  elements. 


Gas  Burner,  Automatic 

matic.) 


— (See  Burner,  Auto- 


WORDS,  TERMS  AND  PHRASES.  803 

Gas  Jet  Photometer. — A  photometer  for  determining 
the  intensity  of  gas  light  by  measuring  the  length  of  the  gas 
jet  producing  the  light  when  burning  under  certain  circum- 
stances. 

Gas  Lighting,  Electrie Various  devices 

employed  ''or  the  simultaneous  electric  ignition  of  a  number 
of  gas  jets  from  a  distance. 

Such  devices  are  operated  by  means  of  minute  electric 
sparks  which  are  caused  to  pass  through  the  escaping  gas  jets. 

The  spark  for  this  purpose  is  obtained  either  by  means  of 
the  extra  current  from  a  spark  coil,  by  means  of  an  induc- 
tion coil  or  by  static  discharges.  (See  Extra  Current.  Spark 
Coil.  Induction  Coil.) 

Gases,  Oeelusion  of —(See  Occlusion  of  Gases,) 

Gastroscope. — An  electric  apparatus  for  the  illumination 
and  inspection  of  the  human  stomach. 

The  light  is  obtained  by  means  of  a  platinum  spiral  in  a 
glass  tube  surrounded  by  a  layer  of  water  to  prevent  undue 
heating1.  The  platinum  spiral  is  placed  at  the  extremities 
of  a  tube,  provided  with  prisms,  and  passed  into  the 
stomach  of  the  patient.  A  separate  tube  for  the  supply  of  air 
for  the  extensior  of  the  stomach  is  also  provided. 

Gauge,  Electrometer A  device  employed  in 

connection  with  some  of  Sir  Win.  Thomson's  electrometers  to 
ascertain  whether  the  needle  connected  with  the  layer  of  acid 
that  acts  as  the  inner  coating  of  the  Leyden  jar  used  in  con- 
nect ion  therewith,  is  at  its  normal  potential. 

The  gauge  consists,  as  shown  in  Fig.  226,  of  an  attracted 
disc  electrometer.  The  attracted  disc  is  shown  above  in  the 
cover  plate  at  S,  and  the  attracting  disc  at  B,  insulated  by  rod 
A,  but  electrically  connected  by  the  wire  C  to  the  sulphuric 
acid  in  the  Leyden  jar. 

Gauge,  \Vire (See  Wire  Gauge.) 

Gauss. — The  unit  of  intensity  of  magnetic  field. 


304 


A  DICTIONARY  OP  ELECTRICAL 


The  term  gauss  for  unit  of  intensity  of  magnetic  field  was 
proposed  by  S.  P.  Thompson  as  being  that  of  a  field  whose  in- 
tensjty  is  equal  to  108  C.  G.  S.  units.  J.  A.  Fleming  pro- 
poses for  the  value  of  the  gauss  such  a  strength  of  field  as 
would  develop  an  electro-motive  force  of  one  volt,  in  a  wire 
one  million  centimetres  in  length,  moving  through  such  a 
field  with  unit  velocity. 

Fleming's  value  for  the  gauss  was  assumed  on  account  of 
the  small  value  of  the  gauss  proposed  by  S.  P.  Thompson.  It 
is  100  times  greater  in  value  than  Thompson's  gauss. 

Sir  Wm.  Thomson  proposes  for  the  value  of  the  gauss  such 
an  intensity  of  magetic  field  as  is  produced  by  a  current  of  one 
(ampere)  weber  at  the  distance  of  one  centimetre. 


Fig.  226. 

Geisslcr  Tubes.— Vacuum  tubes  of  glass,  provided  with 
platinum  electrodes  which  are  passed  through  and  fused  into 
the  glass,  and  designed  to  show  the  various  luminous  effects 
of  electric  discharges  through  comparatively  low  vacua. 

Geissler  tubes  are  made  of  a  great  variety  of  shapes,  and 
often  include  tubes,  spirals,  spheres,  etc,,  within  other 
tubes.  These  inclosed  tubes  are  made  either  of  ordinary  glass, 
or  of  uranium  glass  in  oi'der  to  obtain  the  effects  of  fluor- 
escence, or  some  of  the  inclosed  tubes  are  filled  with  fluoi*- 
escent  liquids. 


WORDS,  TERMS  AND  PHRASES.  305 

The  vacuum  in  Geissler  tubes  is  by  no  means  what  might 
be  called  a  high  vacuum.  Indeed,  if  the  exhaustion  of  the 
tube  be  pushed  too  far,  much  of  the  brilliancy  of  the  luminous 
effects  are  lost. 

Two  of  the  many  forms  of  Geissler  tubes  is  shown  in  Fig.  227. 

Generator,  Dynamo-Electric An  appa- 
ratus in  which  electricity  is  produced  by  the  mechanical  move- 
ment of  conductors  in  a  magnetic  field  so  as  to  cut  the  lines 
of  force. 

A  dynamo-electric  machine.  (See  Dynamo-Electric  Ma- 
chine.) 

Generator,  Pyro-lttagnctic An  appara- 
tus in  which  electricity  is  produced  by  the  combined  action  of 
heat  and  magnetism.  (See  Pyro-Magnetic  Generator.) 


Qfa— r     '       . 


Fig.  227. 

Generator,  Secondary (See  Secondary  Gene- 
rator.) 

Geographical  Equator.  (See  Equator,  Geographical.) 

Geographical  Meridian.  (See  Meridian,  Geograph- 
ical.) 

Gilding,  Electric The  electrolytic  deposition 

of  gold  on  any  object. 

The  object  to  be  gilded  is  rendered  a  conductor  on  its  sur- 
face and  connected  to  the  negative  terminal  of  a  voltaic  cell  or 
other  source,  and  immersed  in  a  plating  bath  containing  a  so- 


306  A  DICTIONARY  OF  ELECTRICAL 

lution  of  a  salt  of  gold,  opposite  a  plate  of  gold  connected  with 
the  positive  terminal  of  the  source.  The  objects  to  be  plated 
thus  becomes  the  kathode,  and  the  plate  of  gold  the  anode  of 
the  plating  bath.  On  the  passage  of  the  current,  the  gold  is 
dissolved  from  the  plate  at  the  anode  and  deposited  on  the  ob- 
ject at  the  kathode.  (See  Kathode.  Anode.) 

Gimbals. — Concentric  rings  of  brass,  suspended  on  pivots 
in  a  compass  box,  and  on  which  the  compass  card  is  supported 
so  as  to  enable  it  to  remain  horizontal  notwithstanding  the 
movements  of  the  ship.  (See  Azimuth  Compass.) 

Each  ring  is  suspended  on  two 
pivots  which  are  directly  opposite 
each  other,  that  is,  at  the  ends  of  a 
diameter,  but  this  diameter  in  one 
ring  is  at  right  angles  to  that  in  the 
other. 


Globular    Lightning.— A 

variety  of  lightning  in  which  the 
electricity  appears  in  the  form  of 
a  ball  or  globe  which  floats  quietly 
about,  and  at  last  explodes  with  a 
loud  detonation. 

Its  cause  is  but  little  understood. 

The  actual  existence  of  these  balls  or  globes  is  doubted  by 
some,  who  regard  them  as  optical  effects  produced  by  the  per- 
sistence of  the  optical  impression  of  a  discharge. 

Glow  Discharge.    (See  Discharge,  Convective.) 
'  Gold  Bath.    (See  Baths,  Gold,  etc.) 

Gold-Leaf  Electroscope.— An  electroscope  in  which 
two  leaves  of  gold  are  used  to  detect  the  presence  of  an  electric 
charge,  or  to  determine  its  character  whether  positive  or  ne- 
gative. 

When  a  charge  is  Imparted  to  the  knob  C,  Fig.  228,  the 


WORDS,  TERMS  AND  PHRASES.  307 

gold  leaves  n,  n,  diverge.  This  will  occur  whether  the  charge 
be  positive  or  negative. 

To  determine  the  polarity  of  an  unknown  chai'ge,  the  leaves 
are  first  caused  to  diverge  hy  means  of  a  known  positive  or 
negative  charge.  The  unknown  charge  is  then  given  to  the 
leaves.  If  they  diverge  still  further,  then  the  charge  is  of  the 
name  name  as  that  originally  possessed  by  the  leaves.  If, 
however,  they  first  move  togetlier  and  are  then  i-epelled,  the 
charge  is  of  the  opposite  name. 

Governor,  Centrifugal  (See  Centrifugal  Gov- 
ernor.) 

Governor,  Electric  SI  cam A  device  used 

in  connection  with  a  valve  to  so  electrically  regulate  the 
supply  of  steam  to  an  engine,  that  the  engine  shall  be  driven 
at  such  a  speed  as  will  maintain  either  a  constant  current  or  a 
constant  potential. 

In  the  electric  governor  the  steam  valve  is  operated  by  an 
electro  magnet,  whose  coils,  in  the  case  of  a  constant  current 
nuirhine,  are  of  thick  wire  and  are  in  the  main  circuit,  and  in 
that  of  a  constant  potential  machine  are  of  thin  wire  and  are 
in  a  shunt  around  the  mains. 

Governors,  Electric Devices  for  electrically 

controlling  the  speed  of  a  steam  engine,  the  direction  of  cur- 
rent in  a  plating  bath,  the  speed  of  an  electric  motor,  the  re- 
sistance of  an  electric  circuit,  the  flow  of  water  or  gas  into  or 
from  a  vessel,  or  for  other  similar  purposes. 

The  particular  form  assumed  by  the  apparatus  varies  with 
the  character  of  the  work  it  is  intended  to  accomplish.  In 
some  cases  ordinary  ball  centrifugal  governors  are  employed 
to  open  or  close  a  circuit ;  or,  a  mass  of  mercury  in  a  rotating 
vessel  is  caused  at  a  certain  speed  to  open  or  close  a  circuit ; 
or,  the  resistance  of  a  bundle  of  carbon  discs  is  caused  to  vary, 
either  by  pressure  produced  by  centrifugal  force;  or  by  the 
movement  of  an  armature. 


308  A  DICTIONARY  OF  ELECTRICAL 

Gramme. — A  weight  equal  to  15.43235  grains.  (See  Metric 
System  of  Weights  and  Measures.) 

Gramme  Atom. — (See  Atom,  Gramme.) 
Gramme  Molecule.— (See  Molecule,  Gramme.) 

Gramophone. — An  apparatus  for  the  recording  and  re- 
production of  articulate  speech.  (See  Phonograph.) 

Graphite.— A  soft  variety  of  carbon  suitable  for  writing 
on  paper  or  similar  surfaces. 

Graphite  is  the  material  that  is  employed  for  the  so-called 
black  lead  of  lead  pencils.  It  is  sometimes  called  plumbago. 
Strictly  speaking  the  term  graphite  is  only  applicable  to  the 
variety  of  plumbago  suitable  for  use  in  lead  pencils. 

Graphite  is  used  for  rendering  surfaces  to  be  plated  electric- 
ally conducting,  and  also  for  the  brushes  of  dynamos  and 
motors. 

Graphophone. — An  apparatus  for  the  recording  and  re- 
production of  articulate  speech.  (See  Phonograph.) 

Gravitation. — A  name  applied  to  the  force  which  causes 
masses  of  matter  to  tend  to  move  towards  each  other. 

This  motion  is  assumed  to  be  that  of  attraction,  that  is,  the 
bodies  are  assumed  to  be  drawn  together.  It  is  not  impos- 
sible, however,  that  they  may  be  pushed  together. 

Gravitation,  like  electricity,  is  well  known,  so  far  as  its 
effects  are  concerned  ;  but,  as  to  the  true  cause  of  either,  par- 
ticularly the  former,  we  are  in  comparative  ignorance. 

The  general  facts  of  gravitation  may  be  succinctly  stated  by 
the  following  law  : 

Every  particle  of  matter  in  the  universe  is  attracted  by 
every  other  particle  of  matter,  and  itself  attracts  every  other 
particle  of  matter,  with  a  force  which  is  directly  proportional 
to  the  product  of  the  masses  of  the  two  quantities  of  matter 
and  inversely  proportional  to  the  square  of  the  distance 
between  them. 


WORDS,  TERMS  AND  PHRASES. 


—The  centre  of  weight  of  a 


Gravity,  Centre  of 

body. 

Bodies  supported  at  their  centres  of  gravity  are  in  equili- 
brium, since  their  weight  is  then  evenly  distributed  around  the 
point  of  support. 

Grcnet's  Voltaic  Cell.— ( Cell,  Voltaic.} 

Grid. — A  lead  plate  in  the  form  of  a  gridiron,  i.  e.,  pro- 
vided with  perforations, 

and  employed  in  storage 
cells  for  the  support  of 
the  active  material.  (See 
Secondary  Cells.) 

Grothiiss*  Hypo- 
thesis.— A  hypothesis 
devised  by  Grothiiss  to 
account  for  the  electroly- 
tic phenomena  that  occur 
on  closing  the  circuit  of  a 
voltaic  cell. 

This  hypothesis  as- 
sumes 

(1)  That  before  the  cir- 
cuit is  closed,  the  mole- 


Fig.  229. 


cules  of  the  electrolyte 
are  arranged  in  an  ir- 
regular or  unpolarized  condition,  asrepresented  in  Fig.  229. 

These  molecules  are  shaded,  as 
shown  in  Fig.  230,  to  indicate  their 
composition  and  polarity. 

(2)  When  the  circuit  is  closed,  and 
a  current  begins  to  pass,  a  polariza- 
tion of  the  electrolyte,  as  shown  at  (2), 
ensues,  whereby  all  the  negative 
ends  of  the  molecules  of  hydrogen  sulphate,  or  sulphuric 
acid,  are  turned  towards  the  positive,  or  the  zinc  plate,  and 


310  A  DICTIONARY  OP  ELECTRICAL 

the  positive  ends,  towards  the  negative,  or  the  copper  plate. 
This,  as  will  be  seen,  will  turn  the  SO4  ends  toward  the  zinc, 
and  the  Ha  ends  towards  the  copper. 

(3)  A  decomposition  of  the  polarized  chain  whereby  the  SO4 
unites  with  the  zinc,  forming  Zn  SO4,  and  the  H2  liberated 
reunites  with   the  SO4   of  the  molecule  next  to   it  in  the 
chain,  and  its  liberated  Hz  with  the  one  next  to  it,  until  the 
last  liberated  H2  is  given  off  at  the  surface  of  the  copper  or 
negative  plate.     This  leaves  the  chain  of  molecules  as  shown 
at  (3). 

(4)  A  semi-rotation  of  the  molecules  of  the  chain  as  at  (3), 
until  they  assume  the  position  shown  at  (4).     This  rotation 
is  required  since  the  molecules  in  (3)  are  turned  with  their 
similar  poles  towards  similarly  charged  battery  plates. 

Ground  or  Earth-Grounded  Wire.— The  earth  or 
ground  which  forms  part  of  the  return  path  of  an  electric  cir- 
cuit. 

A  circuit  is  grounded  when  it  is  completed  in  part  by  the 
ground  or  earth. 

Grounded  Circuit.— (See  Circuit,  Grounded.) 
Grove'§  Voltaic  Cell.— (See  Cell,  Voltaic.) 

Gutta-Perclia. — A  resinous  gum  obtained  from  a  tropical 
tree,  and  valuable  electrically  for  its  high  insulating  powers. 

Gutta-percha  readily  softens  by  heat,  but  on  cooling  be- 
comes quite  hard  and  tough.  Unlike  india  rubber,  it  possesses 
but  little  elasticity.  Its  specific  inductive  capacity  is  4.2, 
that  of  air  being  1,  and  of  vulcanized  india  rubber  2.94.  (See 
Capacity,  Specific  Inductive.) 

Gymnotus  Electricus  .—The  electric  eel  (See  Eel,  Elec- 
tric.) 

Hail,    Assumed     Electric    Origin     of A 

hypothesis,  now  generally  rejected,  framed  to  explain  the 
origin  of  the  alternate  layers  of  ice  and  snow  in  a  hail  stone, 


WORDS,  TERMS  AND  PHRASES.  311 

by  the  alternate  electric  attractions  and  repulsions  of  the 
stones  between  neighboring,  oppositely  charged,  snow  and 
rain  clouds. 

It  is  now  generally  recognized  that  the  electric  manifesta- 
tions attending  hail  storms,  are  the  effects  and  not  the  causes 
of  the  hail.  (See  Paragreles.) 

Hair,  Electrolytic  Removal  of The  per- 
manent removal  of  hair  by  the  electrolytic  destruction  of  the 
hair  follicles. 

A  negative  platinum  electrode  is  inserted  in  the  hair  follicle 
and  the  positive  electrode,  covered  with  moist  sponge  or 
cotton,  is  held  in  the  hand  of  the  patient.  A  current  of  two 
to  four  milliamperes  from  a  battery  of  from  eight  to  ten 
Leclanche  elements  is  then  passed  for  from  ten  to  thirty  sec- 
onds. A  few  bubbles  of  gas  appear,  and  the  hairs  are  then 
removed  from  the  follicle  by  a  pair  of  forceps.  (See  Milliam- 
peres.) 

When  the  work  is  properly  done  there  is  no  destruction  of 
the  skin  and  therefore  no  marks  or  scars. 

In  the  removal  of  hair  from  the  face,  it  is  preferable  that 
the  current  should  slowly  reach  its  maximum  strength. 

Hall  Effect.— (See  Effect,  Hall) 

Hanger-Board  of  Electric  Lamp.— A  board  furnished 
with  a  hand  switch  and  hooks  for  connecting  it  with  a  circuit, 
and  provided  with  means  for  readily  placing  an  arc  lamp  in 
the  circuit. 

The  lamp  is  connected  by  the  mere  act  of  hanging  it  in 
position,  though  binding  posts  ai-e  generally  connected  with 
the  board,  for  the  purpose  of  more  thoroughly  connecting  the 
lamp  terminals  with  the  circuit. 

Hanger,  Cable or  Clip.— (See  Cable  Clip.) 

Harmonic  Receiver. — (See  Receiver,  Harmonic.) 

Harmonic  Telegraphy.— (See  Telegraphy,  Harmonic.) 

Head  Light,  Locomotive  Electric An 


312  A  DICTIONARY  OF  ELECTRICAL 

electric  light  placed  in  the  focus  of  a  parabolic  reflector  in 
front  of  a  locomotive  engine.  (See  Light  House  Illumina- 
tion.) 

Heat. — A  form  of  energy. 

The  phenomena  of  heat  are  due  to  a  vibratory  motion  im- 
pressed on  matter  by  the  action  of  some  form  of  energy. 

Heat  in  a  body  is  due  to  the  vibrations  or  oscillations  of  its 
molecules.  Heat  is  transmitted  through  space  by  means  of 
a  wave  motion  in  the  universal  ether.  This  wave  motion  is 
the  same  as  that  causing  light. 

A  hot  body  loses  its  heat  by  producing  a  wave-motion  in 
the  surrounding  ether.  This  process  is  called  radiation. 

Radiant  Energy,  or  energy  transmitted  by  means  of  ether 
waves,  is  of  two  kinds,  viz.: 

(1)  Obscure  Heat,  or  heat,  which  does  not  affect  the  eye, 
although  it  can  impress  a  photographic  image  on  a  sufficiently 
sensitive  photographic  plate. 

(2)  Luminous  Heat,  or  heat  which  accompanies  light. 
Heat  is  conducted,   or  transmitted  through  bodies,   with 

different  degrees  of  readiness. 

Some  bodies  are  good  conductors  of  heat,  others  are  poor 
conductors. 

Heat  is  transmitted  through  the  mass  of  liquids  by  means  of 
currents  occasioned  by  differences  in  density  caused  by  differ- 
ences of  temperature.  These  currents  are  called  convection 
currents. 

Heat  is  measured  as  to  its  relative  degree  of  intensity  by  the 
thermometer.  It  is  measured  as  to  its  amount  or  quantity  by 
the  calorimeter.  (See  Thermometer.  Calorimeter.) 

The  heat  unit  is  the  calorie,  or  the  amount  of  heat  required 
to  raise  one  gramme  of  water  one  degree  centigrade. 

Another  heat  unit,  very  generally  employed  in  the  United 
States  and  England,  is  the  quantity  of  heat  required  to  raise 
one  pound  of  water  1°  Fahrenheit.  (See  Calorie.  Heat  Unit, 
English.  Joule.  Volt- Coulomb.) 


WORDS,  TERMS  AND  PHRASES.  313 

Heat,  Absorption  and  Generation  of  in 

Voltaic  Cells.— The  heat  effects  which  attend  the  action  of 
a  voltaic  cell. 

The  chemical  solution  of  the  positive  plate  or  element  of  a 
voltaic  cell,  like  all  cases  of  chemical  combination,  is  attended 
by  a  development  of  heat. 

When,  however,  the  circuit  of  the  cell  is  closed,  the  energy 
liberated  during  the  chemical  combination,  appeal's  as  elec- 
tricity, which  develops  heat  in  all  parts  of  the  circuit.  (See 
Heat,  Electric.  Cell,  Voltaic.-) 

Heat,  Atoinie A  constant  product  obtained  by 

multiplying  the  specific  heat  of  an  elementary  substance  by 
its  atomic  weight.  (See  Atomic  Weight.) 

The  product  of  the  specific  heat  of  all  elementary  substances 
by  their  atomic  weights  is  nearly  tho  same.  This  product  is 
called  the  atomic  heat,  and  is  about  equal  to  6.4. 

If,  therefore,  a  number  of  grammes  of  any  substance,  such 
for  example  as  chlorine,  be  taken  numerically  equal  to  its 
atomic  weight,  viz.,  35.5,  this  number,  called  the  gramme 
atom  of  chlorine,  will  represent  the  number  of  small  calories 
of  heat  required  to  raise  one  gramme-atom  of  such  substance 
through  1°  C.  (See  Calorie.) 

Heat,  Electric The  heat  developed  by  the  pass- 
age of  the  electric  current  through  any  conductor. 

Heat  is  developed  by  the  passage  of  the  current  through 
any  conductor,  no  matter  what  its  resistance  may  be. 

If  the  conductor  is  of  considerable  length,  and  of  good  con- 
ducting power,  the  heat  developed  is  not  very  sensible  since 
it  is  spread  over  a  considerable  area,  and  is  rapidly  lost  by 
radiation.  (See  Heat.) 

H,  the  heat  generated  in  any  conductor  of  a  resistance  R, 
by  the  passage  through  it  of  an  electric  current  C,  is  equal  to 
H  =  C8  R,  in  watts. 

But  one  watt  =  .  24  small  calorie  per  second. 


314  A  DICTIONARY  OF  ELECTRICAL 

Therefore,  the  heat  which  is  generated, 

H  =  C  3  R  x  .24  calories  per  second. 

For  the  case  of  a  uniform  wire  of  circular  cross  section  the 
resistance  R,  in  ohms,  is  directly  proportional  to  the  length 
Z,  and  inversely  proportional  to  the  area  of  cross  section 
nr  2,  or 

I  fl.\ 

R  = ;  that  is,  H  =  C3  ( )    • 

Ttr*,  \XT** 

The  temperature  to  which  a  wire  of  a  given  resistance  is 
raised,  will  of  course  vary  with  the  mass  of  the  wire,  its  radia- 
ting surface,  and  its  specific  heat  capacity.  If  the  same  num- 
ber of  heat  calories  are  generated  in  a  small  weight  of  a  conduc- 
tor, whose  radiating  surface  is  small,  the  resulting  temperature 
will  of  course  be  far  higher  than  if  generated  in  a  larger 
mass  provided  with  a  much  greater  radiating  surface.  In 
general,  however,  its  temperature  increases  as  the  square  of 
the  current  strength,  and  as  the  resistance  of  the  wire  per 
unit  of  length  is  greater. 

The  temperature  a  wire  acquires  by  the  passage  of  a  current 
through  it  varies  with  the  tliird  power  of  the  radius.  If  two 
wires  of  the  same  material  have  the  same  lengths,  but  differ- 
ent radii,  the  temperature  acquired  by  the  passage  of  an  elec- 
tric current  wiM  depend  on  the  heat  developed  per  second 
less  that  radiated  per  second.  Since  the  former  varies  as 
1 
— ,  and  the  latter  as  r,  that  is,  as  I  x  27fr,  the  temperature 

r2 

1  1 

attained   varies  as  — ,  and    not   as  — ,  as  frequently  stated. 

rs  ra 

(Larden.) 

The  current  required  to  raise  the  temperature  of  a  bare 
copper  wire  a  given  number  of  degrees  above  the  tempera- 
ture of  the  air  is  given  in  the  following  table 


WORDS,  TERMS  AND  PHRASES. 


315 


Bare  Copper  Wires. 

Cnrsent  required  to  increase  the  temperature  of  a  copper  wire  t°  centigrade 
above  the  surrounding  air,  the  copper  wire  being  bright  polished,  or  blackened. 


Diameter  in 
Centimetres 
and  Mils 
(thousanths 
of  an  inch.) 

CURRENT  IN  AMPERES. 

t.  =  1°  c. 

t.  -  9°  c. 

t.  =  25°  C. 

t.  =  49°  c. 

t.  =  81°  c. 

Cm. 

Mills. 

Brght 

Black 

Brght 

Black 

Brght 

Black 

Brght 

Black 

Brgh 

Black 

.1 

40 

1.0 

1.4 

3.0 

4.1 

4.8 

6.6 

6.5 

8.9 

7.9 

11.0 

.2 

80 

2.8 

3.9 

8.3 

11.5 

13.5 

18.7 

18.3 

25.3 

22.4 

31.0 

.3 

130 

5.2 

7.2 

15.3 

21.2 

24.9 

34.4 

33.5 

46.4 

41.2 

57.0 

.4 

IfiO 

8.0 

11.0 

23.6 

32.7 

38.3 

53.0 

51.7 

71.5 

63.4 

87.8 

.5 

200 

11.1 

15.4 

33.0 

45.7 

53.5 

74.1 

72.2 

99.9 

88.6 

123 

.6 

240 

14.6 

20.3 

43.4 

60.0 

70.3 

97.4 

94.9 

131 

116 

161 

.7 

280 

18.5 

25.6 

54.6 

75.6 

88.7 

123 

119 

165 

147 

203 

.8 

310 

22.6 

31.2 

66.7 

92.4 

108 

150 

146 

203 

179 

248 

.9 

350 

26.9 

37.3 

79.6 

110 

129 

179 

TT4 

241 

214 

296 

1.0 
2.0 

390 
790 

31.5 
89.2 

43.6 
123 

93.3 
264 

129 
365 

151 

428 

210 
593 

204 

577 

283 
799 

251 
709 

347 

t 
981 

3.0 

1180 

164 

227 

485 

671 

787 

1090 

1061 

1468 

1303 

1805 

4.0 

1570 

252 

349 

746 

1035 

1211 

1675 

1633 

2260 

2006 

2776 

5.0 

1970 

353 

488 

1043 

1444 

1692 

2343 

2283 

3160 

2802 

3880 

6.0 

2360 

463 

642 

1371 

1898 

2225 

3080 

WOO 

4154 

3685 

5100 

7.0 

2760 

584 

808 

1728 

2392 

2803 

3882 

3781 

5233 

4642 

6426 

8.0 

3150 

714 

988 

2110 

2922 

3422 

4741 

4620 

0396 

5671 

7850 

9.0 

3540 

8E1 

1178 

2519 

J486 

4088 

5659 

5511 

"630 

6769 

9370 

10.0 
34.4 

3940 

997 

1380 

2950 

4081 

4788 

6626 

6425 

8935 

7926 

10973 

70000 

(Forbes.) 


316  A  DICTIONARY  OF  ELECTRICAL 

Heat,  Molecular The  number  of  calories  of  heat 

required  to  raise  the  temperature  of  one  gramme-molecule  of 
any  substance  1°  C.     (See  Heat,  Atomic.) 

Heat,  Specific The  capacity  of  a  substance  for 

heat  as  compared  with  the  capacity  of  an  equal  quantity  of 
water  for  heat. 

Different  amounts  or  quantities  of  heat  are  required  to  raise 
the  temperature  of  a  given  weight  of  different  substances 
through  one  degree.  The  specific  heats  of  substances  are 
generally  compared  with  water  or  with  hydrogen,  the  capa- 
city of  these  substances  for  heat  being  very  great. 

The  specific  heat  of  all  elementary  atoms  is  the  same. 
For  example,  the  heat  energy  of  an  atom  of  hydrogen  is 
equal  to  that  of  an  atom  of  oxygen,  but  since  the  latter  weighs 
sixteen  times  as  much,  a  given  mass  of  hydrogen  contains 
sixteen  times  as  many  atoms  as  an  equal  mass  of  oxygen ; 
therefore,  when  compared  weight  for  weight,  hydrogen  has  a 
specific  heat  sixteen  times  greater  than  that  of  oxygen. 

Or,  in  general,  comparing  equal  weights,  the  specific  heat 
of  an  elementary  substance  is  inversely  proportional  to  its 
atomic  weight.  (See  Calorimeter.) 

Heat,    Specific of  Electricity.— (See  Specific 

Heat  of  Electricity.) 

Heat  Unit,  English,  or  British  Thermal  Unit.— 
The  quantity  of  heat  required  to  raise  the  temperature  of  one 
pound  of  water  1°  F. 

This  heat  unit  represents  an  amount  of  work  equivalent  to 
772  foot-pounds.    (See  Mechanical  Equivalent  of  Heat.) 
1  Foot  Pound  =  13,562,600  Ergs.     (See  Erg.) 

Heat  Unit,  or  Caloric.— The  quantity  of  heat  required 
to  raise  the  temperature  of  one  gramme  of  water  1°  C. 

The  calorie  is  sometimes  taken  as  the  amount  of  heat  re- 
quired to  raise  the  temperature  of  1,000  grammes  of  water 
1°  C.  These  are  termed,  respectively,  the  Small  Calorie  and 
the  Large  Calorie.  (See  Calorie.) 


WORDS,  TERMS  AND  PHRASES.  317 

Heat  Unit,  or  Joule.— The  quantity  of  heat  developed 
by  the  passage  of  a  current  of  one  ampere  through  a  resis- 
tance of  one  ohm.  (See  Joule.) 

1  Joule  =  .24  Calorie. 

1  Foot  Pound  =  1.356  Joule. 

Heater,   Electric A  device  for  the  conversion 

of  electricity  into  heat  for  the  purposes  of  artificial  heating. 

Electric  heaters  consist  essentially  of  coils  or  circuits  of 
some  refractory  substance  of  high  resistance,  through  which 
the  current  is  passed.  These  coils  or  circuits  are  surrounded 
by  air  or  finely  divided  solids,  and  placed  inside  metallic  boxes, 
or  radiators,  which  throw  off  or  radiate  the  heat  produced. 

When  employed  for  the  heating  of  liquids  the  coils  are 
placed  directly  in  the  liquid  to  be  heated,  or  are  surrounded 
by  radiating  boxes  that  are  placed  in  the  liquid. 

Heating  Effects  of  Currents.— (See  Heat,  Electric. 
Calorimeter,  Electric.  Joule's  Laws.) 

Hccto  (as  a  prefix.) — One  hundred  times. 

Helices,  Sinistrorsal  and  Dextrorsal Coils 

of  wire  so  wrapped  or  wound  that  when  traversed  by  an  elec- 
tric current  they  acquire  all  the  properties  of  magnets.  (See 
Solenoids,  Sinistrorsal  and  Dextrorsal.) 

Heliograph. — An  instrument  for  telegraphic  communica- 
tion by  means  of  flashes  of  light,  which  represent  the  dots  and 
dashes  of  the  Morse  alphabet,  or  the  movements  of  the  needle 
of  the  needle  telegraph  to  the  right  or  left.  (See  Alphabet 
Telegraphic.) 

The  flashes  of  light  are  thrown  from  the  surface  of  a  plane 
mirror.  Motions  to  the  right  or  left  may  be  used  to  distinguish 
between  the  dots  and  dashes,  or  the  same  purpose  may  be 
effected  by  the  relative  durations  of  the  flashes  of  light,  or  by 
the  intervals  between  successive  flashes. 

Similar  telegraphic  communication  has  been  carried  on  be- 
tween steamers  during  foggy  weather  by  means  of  their  fog 
horns,  or  between  locomotives,  by  their  steam  whistles. 


318  A  DICTIONARY  OF  ELECTRICAL 

Hermetical  Seal.— Such  a  sealing  of  a  vessel,  designed 
to  hold  -a  vacuum,  or  gaseous  atmosphere  under  pressures 
greater  or  less  than  that  of  the  atmosphere,  as  will  prevent 
either  the  entrance  of  the  external  atmosphere  into  the  vessel, 
or  the  escape  of  the  contained  gas  into  the  atmosphere. 

Hermetical  sealing  may  be  accomplished  either  by  the  use 
of  suitable  cements,  or  by  the  direct  fusion  of  the  walls  of  the 
containing  vessel. 

Heterostatic.— A  term  applied  by  Sir  William  Thomson 
to  an  electrometer  in  which  the  electrification  is  measured  by 
determining  the  attraction  exerted  by  the  charge  to  be 
measured  and  that  of  an  opposite  charge  imparted  to  the  instru- 
ment by  a  source  independent  of  the  charge  to  be  measured. 

This  term  distinguishes  this  electrometer  from  an  idiostatic 
instrument,  or  one  in  which  the  measurement  is  effected  by 
determining  the  repulsion  between'the  charge  to  be  measured 
and  that  of  a  charge  of  the  same  sign  imparted  to  the  instru- 
ment from  an  independent  source.  (See  Electrometer,) 

Hick§'  Automatic  Button  Repeater.— (See  Re- 
peater, Telegraphic). 

Holders  for  Brushes  of  Dynamo  Electric  Ma- 
chines.— A  device  for  holding  the  collecting  brushes  of  a 
dynamo-electric  machine.  (See  Dynamo-Electric  Machines.) 

Holders  for  Carbons  of  Arc  Lamp.— (See  Lamp, 
Electric  Arc.) 

Holders  for  Safety  Fuse.— (See  Fuse,  Safety.) 

Hood  for  Electric  Lamp.— A  hood  provided  for  the 
double  purpose  of  pi'otecting  the  body  of  an  electric  lamp 
from  rain  or  sun,  and  for  throwing  its  light  in  a  general 
downward  direction. 

Hoods  for  arc  lamps  are  generally  conical  in  shape. 

Horizontal  Component  of  Magnetism.  (See  Com- 
ponent, Horizontal,  of  Earth's  Magnetism.) 


WORDS,  TERMS  AND  PHRASES.  319 

Horns.    Following    ami    Leading:, of   Dy- 

iiamo-Electric  machines.— The  edges  or  terminals  of 
the  pole-pieces  of  a  dynamo-electric  machine  from  or  towards 
which  the  armature  is  carried  during  its  rotation. 

According  to  S.  P.  Thompson,  the  following  horns,  b,  d, 
Fig.  231,  are  those  towards  which  the  armature  is  carried  ; 
the  leading  horns,  a,  c,  those  from  which  it  is  carried. 

As  the  change  in  the  magnetic  intensity  is  more  sudden 
when  the  armature  is  moved  from  the  pole  pieces,  and  least 
when  moved  towards  them,  it  is  clear  that  the  leading  horns  in 
a  dynamo-electric  machine,  and  the  following  horns  in  an  elec- 
tric motor,  become 
heated  during  rotation 
by  the  production  of 
e  d  d  y  currents.  (See 
Currents,  Eddy.  Dy- 
namo Electric,  Ma- 
chines. )  • 

Horse  Power. — 
A  commercial  unit  for 
rate  of  doing  work.  Fig.  SSL 

A  rate  of  doing  work  equal  to  33,000  pounds  raised  one  foot 
per  minute,  or  550  pounds  raised  one  foot  per  second. 

A  careful  distinction  must  be  drawn  between  ivork  and 
power.  The  same  amount  of  work  is  done  in  raising  one 
pound  through  ten  feet,  whether  it  be  done  in  one  minute  or 
in  one  hour.  The  power  expended,  or  the  rate  of  doing  work 
is,  however,  quite  different,  being  in  the  former  case  sixty 
times  greater  than  in  the  latter. 

Horse-Power,  Electric • Such  a  rate  of 

doing  electric  work  as  is  equal  to  33,000  foot-pounds  per 
minute,  or  550  foot-pounds  per  second. 

Just  as  one  pound  of  water  raised  through  a  vertical  dis- 
tance of  one  foot  requires  the  expenditure  of  a  foot-pound  of 
energy,  so  one  coulomb  of  electricity  acting  through  the  differ- 


320  A  DICTIONARY  OF  ELECTRICAL 

enee  of  potential  of  one  volt  requires  a  certain  amount  of  work 
to  be  done  on  it.  (See  Coulomb.  Volt.  Potential.) 

This  amount  is  called  a  volt-coulomb  or  joule  and,  measured 
in  foot-pounds,  is  equal  to  .737324  foot-pounds.  The  volt- 
coulomb,  or  the  joule,  is  therefore  the  unit  of  electric  work, 
just  as  the  foot-pound  is  the  unit  of  mechanical  work. 

The  electric  work  of  any  circuit  is  equal  to  the  product  of 
the  volts  by  the  coulombs. 

If  we  determine  the  rate  per  second  at  which  the  coulombs 
pass,  and  multiply  this  product  by  the  volts,  we  have  a 
quantity  which,  represents  the  electrical  power,  or  rate  of 
doing  electrical  work.  But  one  ampere  is  equal  to  one 
coulomb  per  second;  therefore,  if  we  multiply  the  current  in 
amperes  by  the  difference  of  potential  in  volts,  the  product  is 
equal  to  the  electrical  power  or  rate  of  doing  electrical  work. 

The  product  of  an  ampere  by  a,  volt  is  called  a  volt-ampere, 
or  a  watt. 

One  Watt  =  .0013406  Horse-power,  or 

One  Horse-power  =  745.941  Watts. 

O    T^ 

Therefore  the  Electrical  Horse-power  =  -=j^- , 

746 

where  C  =  the  current  in  amperes,  and  E  =  the  difference  of 
potential  in  volts. 

llorsrslioo  Magnet.— A  magnetized  bar  of  steel  or 
iron  bent  in  the  form  of  a  horseshoe,  or  letter  U. 

A  compound  horseshoe  magnet  is  shown  in  Fig.  232.  It 
consists  of  separately  magnetized  plates  placed  with  their 
similar  poles  together. 

A  horseshoe  magnet  possesses  greater  portative  power  than 
a  straight  bar  magnet.  (See  Portative  Power.) 

(1)  Because  its  opposite  poles  are  nearer  together,  and 

(2)  Because  the  magnetic  resistance  of  its  circuit  is  less,  the 
lines  of  magnetic  force  closing  through  the  armature,  and  thus 
concentrating  the  magnetic  attraction  on  the  armature. 

Electro-magnets  are  generally  made  of  the  horseshoe  shape. 


WORDS,  TERMS  AND  PHRASES. 


321 


Human  Body,  Electric  Resistance  of The 

electric  resistance  offered  by  the  human  body. 

Accurate  data  concerning  the  resistance  of  the  human  body 
are  yet  to  be  obtained. 

When  the  electrodes  of  any  source  are  applied  to  the  skin, 
the  resistance  will  necessarily  vary  with  the  size  and  position 
of  the  contacts,  the  nature  of  the  con- 
tacts, the  condition  both  of  the  skin. 
and  the  contacts,  whether  dry  or  moist, 
and  the  pathological  or  other  condition 
of  the  portion  acted  on. 

The  chief  resistance  offered  by  the 
human  body  to  the  passage  of  an  elec- 
tric current  is  the  skin.  It  may  be 
regarded  as  a  protective  covering  so 
far  as  electric  currents  are  concerned. 

The  body  is  composed,  generally 
speaking,  of  solids  and  liquids.  The 
liquids  offer  paths  of  less  resistance 
than  the  solids.  The  blood  and  nerves 
are  probably  the  best  conducting  media 
in  the  body.  The  muscles  offer  a  fair 
conducting  path  from  the  quantity  of 
saline  fluids  they  contain. 

Since  the  human  body,  like  that  of 
all  animals,  is  itself  a  source  of  electric 
currents,   it  is  possible  that  the  pas- 
sage through  it  of  a  current  generated  from  without,  would  of 
itself  greatly  alter  its  electric  resistance. 

Wolfenden  found  the  resistance  in  fifty  healthy  persons, 
measured  under  exactly  similar  conditions,  to  vary  from  4,000 
to  5,000  ohms. 

Certain  diseased  conditions  of  the  body  appear  to  cause  a 
marked  variation  in  what  may  perhaps  be  regarded  as  a  nor- 
mal electric  resistance.  Charcot  made  measurements  in  which 


322  A  DICTIONARY  OF  ELECTRICAL 

it  appears  that  the  resistance  fell  below  the  normal  in  certain 
cardiac  affections,  and  in  Graves'  Disease,  Wolfenden  cor- 
roborates this,  and  in  eighteen  cases  of  undoubted  Graves' 
Disease  the  resistance  was  but  500  to  1,500  ohms.  In  eight  of 
these  it  was  less  than  1,000  ohms.  In  ordinary  goitre,  unlike 
Graves'  Disease  (Exophthalmic  Goitre),  no  variation  of  the 
resistance  was  found.  In  a  case  of  malignant  thyroid  it  was 
as  high  as  8,000  ohms. 

In  some  cases  of  hemiplegia,  it  varied  from  1,300  to  4,000 
ohms.  In  some  of  epilepsy,  from  1,000  to  4,000.  In  three 
cases  of  cerebr'al  softening,  the  resistance  was  about  3,000  ohms 
and  in  one  case  of  paraplegia,  it  was  6,500  ohms,  and  in  one 
case  of  chorea  (adult),  350  ohms.  (Wolfenden.) 

Hydro-Electric  machine,  Armstrong's A 

machine  for  the  development  of  electricity  by  the  friction  of 
condensed  steam  passing  over  a  water  surface. 

Steam  generated  in  a  suitable  boiler,  Fig.  233,  which  is 
insulated,  is  allowed  to  escape  through  a  tortuous  nozzle, 
from  a  series  of  apertures  opposite  a  pointed  comb,  attached 
to  an  insulated  conductor.  The  cooling  of  the  steam  during 
its  passage  through  a  flat  box,  termed  the  cooling  box, 
connected  with  the  nozzles,  causes  a  partial  condensation,  so 
that  the  box  always  contains  a  small  quantity  of  water. 

The  friction  of  the  drops  of  water  against  the  orifice  and 
possibly  their  friction  against  the  water  surface  itself  are  the 
cause  of  the  electricity. 

A  conductor  connected  with  the  pointed  comb  furnishes 
positive  electricity.  The  boiler  f  urnishes  negative  electricity. 
The  hydro-electric  machine  is  not  a  very  economical  source  of 
electricity,  and  is  only  employed  for  experimental  purposes. 
It  was  discovered  accidentally  through  a  shock  given  to  an 
engineer,  who  placed  his  hand  in  a  jet  of  steam  escaping  from 
a  leaking  boiler  he  was  endeavoring  to  mend.  The  causes 
were  first  studied  by  Mr.,  now  Sir  Wm.,  Armstrong,  who,  in 
1840,  devised  the  apparatus  just  described. 


WORDS,  TERMS  AND  PHRASES. 


323, 


Hydrometer  or    Areometer. — An  apparatus  for  de- 
termining the  specific  gravity  of  liquids.     (See  Areometer.) 


Fig.SSS. 

Hydrotasimcter,  Electric  —  —An  elec- 

trically operated  apparatus  designed  to  show  at  a  distance  the 
exact  position  of  any  water  level. 

In  most  forms  a  float  placed  in  the  liquid  and  connected 


324  A  DICTIONARY  OF  ELECTRICAL 

with  an  electric  circuit,  breaks  this  circuit,  and,  at  intervals, 
sends  positive  impulses  into  the  line  when  rising,  and  negative 
impulses  when  falling.  These  are  registered  by  means  of  an 
index  moved  by  a  step-by-step  motion,  positive  currents 
moving  it  in  one  direction,  and  negative  currents  moving 
it  in  the  opposite  direction. 

Hygrometer.— An  apparatus  for  determining  the  amount 
of  moisture  in  the  air. 


— A  provisional  assumption  of  facts  or 
causes,  the  real  nature  of  which  is  unknown,  made  for  the 
purpose  of  studying  the  effects  of  such  causes. 

A  theory  is  a  more  or  less  accurate  expression  of  some  phys- 
ical truth  which  has  been  deduced  from  independently  derived 
laws  and  principles. 

Our  notions  concerning  the  causes  of  electricity  have,  in 
reality,  only  reached  the  stage  of  hypotheses;  they  cannot 
yet  be  properly  considered  as  having  attained  the  dignity  of 
theories. 

Hypothesis,    Double   Fluid   Electric (See 

Double  Fluid  Electric  Hypothesis.} 

Hypothesis,  Single  Fluid  Electric (See  Single 

Fluid  Electric  Hypothesis.) 

Hypsometer.— An  apparatus  for  determining  the  eleva- 
tion of  a  mountain  or  other  place,  by  obtaining  the  exact  tem- 
perature at  which  water  boils  at  such  elevation. 

The  use  of  a  thermometer  to  measure  the  height  of  a  moun- 
tain or  other  elevation  is  based  on  the  fact  that  a  given  de- 
crease in  the  temperature  of  the  boiling  point  of  water  inva- 
riably attends  a  given  decrease  in  the  atmospheric  pressure. 
Therefore,  as  the  observer  goes  further  above  the  level  of  the 
sea,  the  boiling  point  of  water  becomes  lower,  and  from  this 
decrease,  the  height  of  the  mountain  or  other  elevation  may 
be  calculated. 


WORDS,  TERMS  AND  PHRASES.  325 

Idio-Electrics.— A  name  formerly  applied  to  such  bodies 
as  amber,  resins,  glass,  etc.,  which  are  readily  electrified  by 
friction  and  which  were  then  supposed  to  be  electric  in  them- 
selves. 

This  distinction  was  based  on  an  erroneous  conception,  and 
the  word  is  now  obsolete. 

Idio§tatic. — A  term  employed  by  Sir  Wm.  Thomson,  to 
designate  an  electrometer  in  which  the  measurement  is 
effected  by  determining  the  repulsion  between  the  charge  to 
be  measured  and  that  of  a  charge  of  the  same  sign  imparted 
to  the  instrument  from  an  independent  source.  (See  Hetero- 
static.) 

liinilx-r.  JabloclikofT A  small  strip  of  carbon, 

or  carbonaceous  paste  of  readily  ignitable  material,  placed  at 
the  free  ends  of  the  parallel  carbons  of  a  Jablochkoff  candle, 
for  the  establishment  of  the  arc  on  the  passage  of  the  current. 

The  igniter  is  necessary  in  the  Jablochkoff  electric  candle, 
since  the  parallel  carbons  are  rigidly  kept  at  a  constant 
distance  apart  by  the  insulating  material  placed  between 
them,  and  cannot  therefore  be  moved  together  as  in  the  case 
of  the  ordinary  lamp.  (See  Candle,  Jablochkoff.) 

Ignition,  Electric The  ignition  of  a  combus- 
tible material  by  heat  of  electric  origin. 

The  electric  ignition  of  wires  is  generally  accomplished  by 
electric  incandescence.  Ignition  may  be  accomplished  by 
the  heat  of  the  voltaic  arc.  (See  Heat,  Electric.  Furnace, 
Electric.) 

The  ignition  of  combustible  gases  is  accomplished  by  the 
heat  of  the  electric  spark.  (See  Burner,  Automatic  Electric.) 

Illumination,  Artificial —The  employment 

of  artificial  sources  of  light  to  render  objects  visible. 

A  good  artificial  illuminant  should  possess  the  following 
properties,  viz.: 

(1)  It  should  give  a  general  or  uniforn  illumination  as  dis- 
tinguished from  sharply  marked  regions  of  light  and  shadow. 


326  A  DICTIONARY  OF  ELECTRICAL 

To  this  end,  a  number  of  small  lights  well  distributed  are  pre- 
ferable to  a  few  large  lights. 

(2)  It  should  give  a  steady  light,  uniform  in  its  brilliancy, 
as  distinguished  from  a  nickering,  unsteady  light.     Sudden 
changes  in  the  intensity  of  a  light  injure  the  eyes  and  prevent 
distinct  vision. 

(3)  It  should  be  economical,  or  not  cost  too  much  to  produce. 

(4)  It  should  be  safe,  or  not  likely  to  cause  loss  of  life  or 
property.     To  this  intent  it  should,  if  possible,  be  inclosed  in 
or  surrounded  by  a  lantern  or  chamber  of  some  incom.bustible 
material,  and  should  preferably  be  lighted  at  a  distance. 

(5)  It  should  not  give  off  noxious  fumes  or  vapors,  when  in 
use,  nor  should  it  unduly  heat  the  air  of  the  space  it  illumines. 

(6)  It  should  be  reliable,   or  not  apt  to  be  unexpectedly 
extingished  when  once  lighted. 

The  claims  of  the  electric  incandescent  lamp  as  a  cheap 
safe,  reliable  and  steady,  artificial  illuminant,  will  be  evident 
if  these  points  are  examined  seriatim,  viz. : 

(1)  The  incandescent  light  is  capable  of  great  sub-division, 
and  can  therefore  produce  a  uniform  illumination. 

(2)  It  is  steady  and  free  from  sudden  changes  in  its  intensity. 

(3)  It  compares  favorably  in  point  of  economy  with  coal  oil 
or  gas. 

(4)  It  is  safer  than  any  known  illuminant,  since  it  can  be 
entirely  inclosed  and  can  be  lighted  from  a  distance,  or  at  the 
burner,  without  the  use  of  the  dangerous  friction  match. 

The  leads,  however,  must  be  carefully  insulated  and  pro- 
tected by  safety  fuses.  (See  Fuse,  Safety. ) 

(5)  It  gives  off  no  gases,  and  produces  far  less  heat  than  a 
gas  burner  of  the  same  candle  power. 

It  perplexes  many  people  to  understand  why  the  incandes- 
cent electric  light  should  not  heat  the  air  of  a  room  as  much 
as  a  gas  light,  since  it  is  quite  as  hot  as  the  gas  light.  It 
must  be  remembered,  however,  that  a  gas  burner,  when 
lighted,  not  only  permits  the  same  quantity  of  gas  to  enter 


WORDS,  TERMS  AND  PHRASES.  327 

the  room  which  would  pass  if  the  gas  were  simply  turned  on 
and  not  lighted,  but  that  this  bulk  of  gas  is  still  given  off,  and 
is  even  considerably  increased,  by  the  combination  of  the  illu- 
minating gas  with  the  oxygen  of  the  atmosphere,  and  which 
moreover,  it  is  given  off  as  highly  heated  gases.  Such  gases 
are  entirely  absent  in  the  incandescent  electric  light,  and  con- 
sequently its  power  of  heating  the  surrounding  air  is  much 
less  than  that  of  gas  lights. 

(6)  It  is  quite  reliable  and  will  continue  to  burn  as  long  as 
the  current  is  supplied  to  it. 

Illumination,    Light  House  Electric.— (See 

Light  House  Illumination,  Electric). 

Illumination,  Unit  of — A  standard  of  illumina- 
tion proposed  by  Preece,  equal  to  the  illumination  on  a  sur- 
face such  as  a  street,  given  by  a  standard  candle  at  the  dis- 
tance of  12.7  inches. 

According  to  Preece,  the  illumination  for  the  average  streets 
of  London,  where  gas  is  employed,  is  equal  to  about  one-tenth 
tliis  standard,  in  the  neighborhood  of  a  gas  lamp,  and  about 
one-fiftieth,  in  the  middle  space  between  two  lamps. 

The  term,  unit  of  illumination,  in  place  of  the  intensity  of 
light,  was  proposed  by  Preece,  in  order  to  avoid  the  very 
great  difficulty  in  determining  the  intensity  of  a  light  in  a 
street  or  space  where  there  were  a  number  of  luminous 
sources,  and  where  the  directions  of  incidence  of  the  different 
lights  vary  so  greatly. 

A  carcel  standard  at  the  distance  of  a  metre  will  illumine 
a  surface  to  the  same  intensity  of  illumination  as  a  standard 
candle  at  the  distance  of  12.7  inches. 

Images,  Electric -A  term  sometimes  applied  to 

the  charge  produced  in  a  neighboring  surface  by  induction 
from  a  known  charge. 

A  positive  charge  produces  by  induction,  in  a  flat  metallic 
surface  near  it,  a  negative  charge  which  is  distributed  with 


828  A  DICTIONARY  OF  ELECTRICAL 

varying  density  over  the  surface,  but  acts  electrically  as  would 
an  equal  quantity  of  negative  electricity  placed  back  of  the 
plate,  at  the  same  distance  the  positive  charge  is  in  front  of  it. 
The  correspondence  of  this  charge  with  the  image  of  an 
object  seen  in  a  plane  mirror  has  led  to  the  term  electrical 
image. 

Maxwell  defines  electric  image  as  follows:  "An  electric 
image  is  an  electrified  point,  or  system  of  points,  on  one  side  of  a 
surface,  which  would  produce  on  the  other  side  of  that  surface 
the  same  electrical  action  which  the  actual  electrification  of 
th^t  surface  really  does  produce." 

Imponderable.— That  which  possesses  no  weight. 

A  term  formerly  applied  to  the  luminiferous  or  universal 
ether,  but  now  generally  abandoned.  It  is  very  questionable 
whether  it  is  possible  for  any  form  of  matter  to  be  actually 
imponderable,  or  to  possess  no  attraction  for  other  matter 

An  imponderable  fluid,  as  for  example  the  universal  ether, 
as  the  term  is  now  generally  employed,  is  a  fluid  whose 
weight  is  comparatively  small  and  insignificant,  and  not  a 
fluid,  an  indefinite  quantity  of  which  would  be  entirely  devoid 
of  weight. 

Incandescence,  Electric The  electric 

heating  of  a  substance,  generally  a  solid,  to  luminosity. 

Electric  incandescence  of  solid  substances  differs  from 
ordinary  incandescence,  in  the  fact  that  unless  the  sub- 
stance is  electrically  homogeneous  throughout,  the  tempera- 
ture is  not  uniform  in  all  parts,  but  is  highest  in  those  por- 
tions where  the  resistance  is  highest  and  the  radiation  small- 
est. The  deposition  of  carbon  in  and  on  a  carbon  conductor 
by  the  flashing  process  is  quite  different  as  performed  by 
electrical  incandescence,  than  it  would  be  if  the  carbons  were 
heated  by  ordinary  furnace  or  other  heat.  (See  Flashing  of 
Carbons.) 

Inclination  Compass,  or  Inclinometer.— A  mag- 
netic needle  so  arranged  as  to  readily  permit  the  measurement 


WORDS,  TERMS  AND   PHRASES.  329 

of  the  magnetic  dip  at  any  place.  (See  Dipping  Circle  or  In- 
clination Compass. ) 

Inclination,  Magnetic —(See  Magnetic  Inclina- 
tion.") 

Inclination  Map  or  Chart.— A  chart  or  map  on  which 
lines  are  drawn  showing  the  lines  of  equal  dip  or  inclination, 
or  the  isoclinic  lines. 

An  inclination  chart  is  shown  in  Fig  234. 

It  will  be  seen  that  the  magnetic  equator,  or  line  of  no  dip, 
does  not  correspond  with  the  geographical  equator,  being 
generally  north  of  the  equator  in  the  eastern  hemisphere,  and 
south  of  it  in  the  western.  The  figures  attached  to  the  lines 
indicate  the  value  of  the  angle  of  dip. 

Inclination  or  Dip  of  Magnetic  \ccdlc.— The 
deviation  of  an  evenly  weighted  magnetic  needle  from  a 
horizontal  position. 

The  direction  of  a  magnetic  needle  in  all  parts  of  the  earth, 
except  at  the  magnetic  equator,  differs  from  a  level  or  hori- 
zontal position.  One  of  its  ends  inclines  or  dips  towards  the 
ground.  (See  Dip,  Magnetic.  Dipping  Needle.) 

India  Rubber. — A  resinous  substance  obtained  from 
the  milky  juices  of  several  tropical  trees. 

India  rubber  is  quite  elastic  and  possesses  high  powers  of 
electric  insulation.  When  vulcanized  or  combined  with 
sulphur,  ifrstill  retains  its  powers  of  electric  insulation  in  a  high 
degree.  In  this  state  it  is  readily  electrified  by  friction.  (See 
Caoutchouc), 

Indicating  Bell.— (See  Bell,  Indicating.) 

Indicator*,  Electric Various  devices,  generally 

operated  by  the  deflection  of  a  magnetic  needle,  or  the  ring- 
ing of  a  bell,  or  both,  for  indicating  at  some  distant  point  the 
condition  of  an  electric  circuit,  the  strength  of  current  that  is 
flowing  through  it,  the  height  of  water  or  other  liquid,  the 
pressure  on  a  boiler,  the  temperature,  the  speed  of  an  engine 


330 


A  DICTIONARY  OP  ELECTRICAL 


WORDS,  TERMS  AND  PHRASES.  33l 

or  line  of  shafting,  the  working  of  a  machine,  or  other  similar 
events  or  occurrences. 

Indicators  are  of  various  forms.  They  are  generally  electro- 
magnetic in  character. 

Indicators,  Electric  Circuit Various  devices, 

generally  in  the  form  of  vertical  galvanometers,  emploj'ed  to 
indicate  the  presence  and  direction  of  a  cui'rent  in  a  circuit, 
and  often  to  roughly  measure  its  strength.  (See  Galvanometer, 
Vertical.) 

Induced  Current,  Direct  Induced  Current. — (See 
Current,  Extra.) 

Induced  Current,  Reverse  Induced  Current. — 
(See  Current,  Extra.) 

Induction  Balance,  Hughes' (See  Balance, 

Induction,  Hughes'.) 

Induction,  Dynamo  Electric (See  Induction, 

Electro-Dynamic.) 

Induction,  Electro-Dynamic Electro  motive 

forces  set  up  by  induction  in  conductors  which  are  either 
actually  or  practically  moved  so  as  to  cut  the  lines  of  magnetic 
force. 

These  electro-motive  forces,  when  permitted  to  act  or  neutral- 
ize themselves,  produce  a  current. 

Electro-dynamic  induction  occurs  only  in  a  magnetic  field, 
the  intensity  of  which  is  either  increasing  or  decreasing. 
It  may  be  produced  in  the  following  ways,  viz.: 

(1)  By  the  use  of  an  inducing  field  of  varying  magnetic  in- 
tensity. 

Varying  the  strength  of  the  current  and  consequently 
the  intensity  of  its  magnetic  field,  will  produce  an  in- 
duction of  the  circuit  on  itself,  or  a  self-induction,  and  will 
reault  in  extra  currents,  which  are  in  the  opposite  direction  on 
closing  and  in  the  same  direction  on  opening  the  circuit ;  or  it 
will  produce  induction  in  neighboring  conductors  which  are 


332  A  DICTIONARY  OF  ELECTRICAL 

within  the  field  of  the  inducing  current.  (See  Self-induction. 
Mutual  Induction.  Currents,  Extra.} 

(2)  By  using  an  inducing  field  of  practically  unvarying 
intensity,  and  varying  the  number  of  lines  of  magnetic  force 
that  pass  through  a  conductor,  by  moving  the  conductor 
through  the  inducing  field  so  as  to  cut  its  lines  of  force. 

Or,  the  conductor  remaining  fixed  in  position,  the  inducing 
field  is  moved  past  the  conductor  by  moving  the  electro-mag- 
net, or  electric  circuit,  or  permanent  magnet  producing  the 
field. 

Electro-dynamiC'induction,  therefore,  includes. 

(1)  Self-induction. 

(2)  Mutual  Induction,  or,  as  it  is  sometimes  called,  Voltaic 
or  Current  Induction. 

(3)  Electro-Magnetic  Induction,  or  Dynamo-Electric  Induc- 
tion. 

(4)  Magneto-Electric  Induction. 


Fig.  235. 

The  coil  B,  Fig.  235,  consists  of  two  parallel  coils  of  insu- 
lated wire,  the  terminals  of  one  of  which,  called  the  primary 
coil,  are  connected  with  the  battery  cell  P  N,  and  those  of  the 
other,  called  the  secondary  coil,  with  the  galvanometer  G. 

Under  these  circumstances  it  is  found: 

(1)  That  at  the  moment  of  closing  the  circuit,  through  the 
primary  coil,  a  momentary  current  is  produced  in  the  second- 
ary coil  in  a  direction  opposite  to  that  of  the  current  through 


WORDS,  TERMS  AND  PHRASES.  333 

the  primary,  as  is  shown  by  the  direction  of  deflection  of  the 
needle  of  the  galvanometer. 

(2)  At  the  moment  of  breaking  the  circuit  through    the 
primary  coil  an  induced  current  is  produced  in  the  secondary 
coil  in  the  same  direction  as  that  flowing  through  the  primary 
coil. 

(3)  These  induced  currents  are  momentary,  and  only  con- 
tinue in  the  secondary  while  the  intensity  of  the  current  in 
the  primary  is  varying,  i.e.,  while  variations  are  occurring  in 
the  strength  of  the  magnetic  field  in  which  the  secondary  coil 
is  placed. 

If,  for  instance,  when  the  current  is  established  in  the 
primary  coil,  and  no  current  exists  in  the  secondary,  the 
intensity  of  the  current  in  the  primary  be  varied  by  establish- 
ing a  shunt  circuit  across  the  battery  terminals,  as  by  placing  a 
short  wire  d,  Fig.  236,  in  the  mei-cury  cups  g,  g,  thus  decreas- 
ing the  intensity  of  the  current  in  the  primary,  an  induced 
current  will  be  set  up  in  the  secondary  circuit  in  the  same 
direction  as  the  primary  current. 


Fig.  SS6. 

From  all  of  these  phenomena  we  see  that  an  increase  of  cur- 
rent in  a  conductor  produces  in  a  neighboring  conductor  an 
induced  inverse  current,  or  one  in  the  opposite  direction  to 
the  inducing  current,  while  a  decrease  of  such  current  pro- 


A  DICTIONARY  OF  ELECTRICAL, 


duces  a  direct  induced  current,  or  one  in  the  same  direction 
as  Ihe  inducing  current. 

If  the  induction  coil  be  made,  as  in  Fig.  237,  with  its  primary 
coil  movable  into  and  out  of  the  secondary  coil,  then  the  fol- 
lowing phenomena  will  occur: 

(1)  When  the  primary  coil  is  moved  towards  the  secondary 
coil  an  inverse  current  is  induced  in  the  secondary,  and, 

(2)  When  the  primary  coil  is  moved  away  from  the  second- 
ary coil  a  direct  current  is  induced  in  the  secondary. 

The  movements  of  permanent  magnets  towards  or  from  a 
coil  will  also  produce  an  induced  current. 

If,  for  example,  the  apparatus  be  arranged,  as  in  Fig.  238, 
then: 


Fig.  337. 

(1)  A  motion  of  the  magnet  towards  the  coil  produces  an 
induced  current  in  the  coil  in  one  direction,  and 

(2)  Its  motion  away  from  the  magnet  produces  an  induced 
current  in  the  coil  in  the  opposite  direction. 


WORDS,  TERMS  AND  PHRASES. 


335 


These  induced  currents  are  respectively  inverse  and  direct 
as  compared  with  the  direction  of  the  amperian  currents  which 
are  assumed  to  produce  the  magnetic  poles  of  permanent  mag- 
nets, or  of  the  currents  that  actually  produce  electro  magnets. 
(See  Magnetism,  Ampere's  Theory.) 

Induction,  Electro-Magnetic  --  (See  Induction 
Electro-Dynamic.  ) 

These  facts  may  be  expressed  by  the  following  laws  : 
(1)  Any  decrease  in  the  number  of  lines  of  force  which  pass 
through  a  circuit  produces  a  direct  current  in  that  circuit, 
while  any  increase  in  the  number  of  such  lines  of  force  which 
pass  through  any  circuit  produces  an  inverse  current  in  that 
circuit. 


(2)  The  induced  current  has  an  intensity,  or  more  correctly, 
the  differences  of  potential  produced  are  proportional  to  the 
rate  of  increase  or  decrease  of  lines  of  force  passing  through 
the  circuit. 

Any  conductor  therefore,  when  moved  through  a  magnetic 
field  so  as  to  cut  the  lines  of  magnetic  force,  will  have  a 
current  produced  in  it  by  induction. 


336 


A  DICTIONARY   OF  ELECTRICAL 


A  simple  but  effective  manner  of  remembering  the  direction 
of  such  currents  is  that  proposed  by  Fleming. 

If  the  hand  be  held  with  the  fingers  extended,  as  in  Fig.  239, 
and  the  direction  of  the  fore  finger  represent  the  positive  direc- 
tion of  the  lines  of  force,  i.  e.,  those  coming  out  of  the  N.  pole 
of  a  magnet,  then,  if  a  wire  or  other  conductor  be  moved  in 
the  direction  in  which  the  thumb  points,  so  as  to  cut  these 
lines  of  force  at  rigbt  angles,  that  is  if  the  conductor  have  its 
length  moved  directly  across  these  lines,  it  will  have  an 
induced  current  developed  in  it  in  the  direction  in  which  the 
middle  finger  points.  (See  Direction  of  Lines  of  Force). 

Or,  the  same  thing  can, 
perhaps,  be  even  more 
readily  remembered  by  cut- 
ting a  piece  of  paper  in  the 
shape  shown  in  Fig.  240, 
marking  it  as  shown,  and 
then  bending  the  arm  P, 
upwards  at  the  dotted  line, 
so  as  to  form  three  axes  at 
right  angles  to  one  an- 
other. 

As  has  been  already  re- 
mai'ked,  a  difference  of 
potential  is  produced  by 
the  motion  of  a  conductor 
through  a  magnetic  field  so 
as  to  cut  its  lines  of  force, 
and  not  a  current. 

It  can  be  shown  that  in 
order  to  generate  a  differ- 
ence  of   potential    of   one 
volt,  100,000,000    C.    G.   S. 
lines  of  force  must  be  cut  per  second. 

In  electro-magnetic  induction  the  induced  current  is  pro- 
duced by  the  energy  absorbed  by  moving  the  conductor  through 


WORDS,  TERMS  AND  PHRASES. 


33T 


the  field.   Lenz  has  shown  that  in  all  cases  of  electro-magnetic 
induction,  produced  by  the  movement  either  of  the  circuit  or 
of  the  magnet,  the  current  induced  in 
the  circuit  is  m  such  a  direction  as  to          , 
produce  a  magnet  pole  which  would   »_,  § 
tend  to  oppose  the  motion.  c  £ 

For  mutual  attraction  and  repulsion   *•  «g 

of  currents  see  Electro-Dynamics.  j«  $ 

Q  ^ 

Induction,  Electrostatic a 

The  production  of  an  electric 


Direction  of 
Motion. 


M. 
charge  in  a  conductor  brought  into  an   "8 

electrostatic  field.  J5 

If  the  insulated  conductor  A  B,  Fig.     g 
241,  be  brought  into  the  positive  elec-    g 
trostatic  field  of  the  insulated  conductor 
C,  then, 

(1)  A  charge  will  be  produced  on  A 

B,  as  will  be  indicated  by  the  divergence  of  the  pith  balls. 

(2)  This  charge  is  negative  at  the  end  A,  nearest  C,  and 
positive  at  the  end  C,  furthest  from  B,  as  can  be  shown  by  an 
electroscope.    (See  Electroscope.) 


fig.  2W>. 


(3)  The  cliarg-es  at  A  and  B,  are  equal  to  each  other;  for,  if  the 
conductor  A  B,  be  removed  from  the  field  of  C,  without  touch- 
ing it,  the  opposite  charges  completely  neutralize  each  other. 


668  A  DICTIONARY  OF  ELECTRICAL 

(4)  If,   however,   the  conductor  A  B,  be  touched  at  any 
place  by  a  conductor  connected  with  the  earth,  it  will  lose  its 
positive  charge,  and  will  r.emain  negatively  charged   when 
removed  from  the  field  of  C.     It  is  in  this  manner  that  the 
electrophones  is  charged.     (See  Elect rophorus. ) 

(5)  The  amount  of  the  charges  produced  in  the  conductor, 
A  B,  can  never  be  greater  than  that  in  the  inducing  body  C. 

That  is  to  say,  the  negative 
electricity  at  A,  may  be 
sufficient  in  amount  to 
neutralize  the  positive 
charge  on  C,  if  allowed  to 
do  so.  In  point  of  fact  the 
charge  induced  is  less  in 
amount  than  the  inducing 
charge,  according  to  the 
Fig.  2«.  distance  between  C  and  A, 

and  the  nature  and  condition  of  the  medium  which  separates 
them. 

The  attractions  of  light  bodies  by  charged  surfaces  is  due  to 
the  opposite  charge  produced  on  those  parts  of  the  light  bodies 
that  are  nearest  the  charged  body. 

The  pith  ball  B,  Fig.  242,  suspended  by  a  silk  thread  between 
an  insulated  positively  charged  conductor  A,  and  the  unin- 
sulated conductor  C,  will  receive  by  induction  a  negative 
charge  on  the  side  nearest  to  A,  and  a  positive  charge  on  the 
side  nearest  to  C.  It  is  therefore  attracted  to  A,  where,  re- 
ceiving a  positive  charge,  it  is  repelled  to  C,  where  it  is  dis- 
charged and  again  assumes  a  vertical  position.  Induction 
again  occurs,  and  consequent  attraction  and  repulsion.  These 
movements  follow  one  another  so  long  as  a  sufficient  charge 
remains  in  A. 

Induction  Coils.— Parallel  coils  of  insulated  wire  em- 
ployed for  the  production  of  currents  by  electro-magnetic  in- 
duction. (See  Induction,  Electro-Magnetic.) 


WORDS,  TERMS   AND   PHRASES. 


339 


A  rapidly  interrupted  battery  current  sent  through  a  coil  of 
wire  called  the  primary  coil,  induces  intermittent  currents  in 
a  coil  of  wire  called  the  secondary  coil. 


As  heretofore  made,  the  primary  coil  consists  of  a  few 
turns  of  a  thick  wire,  and  the  secondary  coil  of  many  turns, 
often  thousands,  of  fine  wire.  Such  coils  are  generally  called 
Rulinikorff  Coils,  from  the  name  of  a  celebrated  manufacturer 
of  them. 

In  the  form  of  Rulinikorff  coil,  shown  in  Fig.  243,  the  pri- 
mary wire  is  wound  on  a  core  formed  of  soft  iron  wires,  and 
its  ends  brought  out  as  shown  at /,  f '.  The  fine  wire  is  wrapped 
around  an  insulated  cylinder  of  vulcanite,  or  glass,  surround- 
ing the  primary  coil.  This  wire  is  very  thin,  and  in  some 
coils  is  over  one  hundred  miles  in  length. 

The  ends  of  the  secondary  coil  are  connected  to  the  insu- 
lated pillars  A  and  B. 

The  primary  current  is  rapidly  broken  by  means  of  a  mer- 
cury break,  shown  at  L,  and  M, 


340  A  DICTIONARY  OF  ELECTRICAL 

The  commutator,  shown  to  the  right  and  front  of  the  base, 
is  provided  for  the  purpose  of  cutting  off  the  current  through 
the  primary,  or  for  changing  its  direction.  When  a  battery 
which  produces  a  comparatively  large  current  of  but  a  few  volts 
electro-motive  force,  is  connected  with  the  primary,  and  its 
current  rapidly  interrupted,  a  torrent  of  sparks  will  pass  be- 
tween A  and  B,  having  an  electro-motive  force  of  many  thou- 
sands of  volts. 

In  such  cases,  excepting  losses  during  conversion,  the  energy 
in  the  primary  current,  or  C  E,  is  equal  to  the  energy  in  the 
secondary  current,  or  C'  E'.  As  much  therefore  as  E',  the 
electro-motive  force  of  the  secondary  current  exceeds  E,  the 
electro-motive  force  of  the  primary  current,  the  current 
strength  C',  of  the  secondary  will  be  less  than  the  current 
strength  C,  of  the  primary.  (See  Converter,  or  Trans- 
former.) 

Fig.  244,  shows  diagramatically  the  arrangement  and  con- 
nection of  the  different  parts  of  an  induction  coil. 

The  core  I,  I'  consists  of  a  bundle  of  soft  iron  wires,  each  of 
which  is  covered  with  a  thin  insulating  layer  of  varnish  or  ox- 
ide. A  primary  wire  P,  P,  consisting  of  a  few  turns  of  com- 
paratively thick  wire  is  wound  around  the  core,  and  a  greater 
length  of  thin  wire  S,  S,  is  wound  upon  the  primary.  This  is 
called  the  secondary.  So  as  not  to  confuse  the  details  of  the 
figure  it  is  represented  as  a  few  turns. 

The  ends  of  the  battery  B  are  connected  to  the  primary 
wire,  through  the  automatic  interrupter,  in  the  manner  shown. 
It  will  be  seen  that  the  attraction  of  the  core  1 1',  for  the  vi- 
brating armature  H,  will  break  contact  at  the  point  o,  and 
cause  a  continued  interruption  of  the  battery  current. 

The  condenser  C,  C',  is  connected  as  shown.  It  acts  to  di- 
minish the  sparking  at  the  contact  points  on  breaking  contact, 
and  thus,  by  making  the  battery  current  more  sudden,  to  con- 
sequently make  its  inductive  action  greater. 


WORDS,  TERMS  AND  PHRASES. 


841 


Induction   Coils,  Inverted 


Conver- 


ter§.  Transformers.— An  inverted  induction  coil  is  an  in- 
duction coil  in  which  the  primary  coil  is  made  of  a  long,  thin 
wire,  and  the  secondary  coil  of  a  short,  thick  wire. 


By  the  use  of  an  inverted  coil,  a  current  of  high  electromo- 
tive force  and  comparatively  small  current  strength,  i.  e.,  but 
of  few  amperes,  is  converted  or  transformed  into  a  current  of 
comparatively  small  electromotive  force  and  large  current 
strength.  For  the  advantages  of  this  see  System  of  Dis- 
tribution by  Alternating  Currents. 

Inverted  induction  coils  are  called  converters  or  transfor- 
mers. (Converter  or  Transformer.) 


—(See  Lateral  Induction.) 
•—The  production  of  mag- 


Inductioii,  Lateral  — 

Induction,  magnetic 

netism  in  a  magnetizable  substance  by  bringing  it  into  a  mag- 
netic field. 

When  a  magnetizable  body  is  brought  into  a  magnetic  field 
the  following  phenomena  occur,  viz. : 


343  A  DICTIONARY  OF   ELECTRICAL 

(1)  The  lines  of  magnetic  force  pass  through  the  body  and 
are  condensed  upon  it.  (See  Field,  Magnetic,  Paramagnetic.) 

(2)  If  the  body  is  free  to  move  around  an  axis,  but  not  bodily 
towards  the  magnet  pole,  it  will  come  to  rest  with  its  greatest 
extent  or  length  in  the  direction  of  the  lines  of  force  ;  i.  e.,  in 
the  direction  in  which  it  will  offer  the  least  resistance  to  the 
lines  of  force  that  thread  through  it. 

(3)  The  body  will  therefore  become  a  magnet,  its  south  pole 
being  situated  where  the  lines  of  force  enter  it,  and  its  north 
pole  where  they  pass  out  from  it. 

(4)  The  intensfty  of  the  induced  magnetism  will  depend  on 
the  number  of  lines  of  force  that  pass  through  it. 

(5)  The  direction  of   the  axis   of  magnetism  will  depend 
on  the  directions  in  which  the  lines  of  force  thread  through  the 
body.    (See  Axis  of  Magnetism). 

If  a  bar  of  iron  N,  S,  _j. 
Fig.  245,  be  brought  near 
the  magnetized  bar,  N,  S, 
poles  will  be  produced  in 
it  by  induction,  as  may  be 
shown  by  throwing  iron  filings  on  it. 

Since  the  nearer  the  body  to  be  magnetized  is  brought  to 
the  magnetizing  pole,  the  greater  will  be  the  number  of  lines 
of  force  that  thread  through  it,  the  greater  will  be  the  inten- 
sity of  its  induced  magnetism.  This  will  be  greatest  when 
the  two  actually  touch  each  other. 

The  production  of  magnetism  therefore  by  contact  or  touch 
is  only  a  special  case  of  magnetization  by  induction. 

The  attraction  of  a  magnetizable  body  by  a  magnet  pole,  is 
caused  by  the  mutual  attraction  which  exists  between  the  un- 
like pole  produced  by  induction  in  the  parts  of  the  piece  of 
iron  nearest  the  attracting  magnet  pole.  This,  it  will  be  seen, 
is  the  same  as  the  attraction  caused  by  an  electric  charge. 

Induction,  magneto  Electric (See  Induction, 

Electro  Dynamic.) 


WORDS,  TEEMS   AND  PHRASES.  343 

Induction,  mutual Induction  produced  by  two 

neighboring-  circuits  on  one  another  by  the  mutual  interac- 
tion of  their  magnetic  fields.  (See  Currents,  Extra.) 

Induction,  Self  —  —Induction  produced   in  a 

circuit  at  the  moment  of  starting-  or  stopping  the  currents 
therein,  by  the  induction  of  the  current  on  itself.  (See  Cur- 
rent, Extra.) 

Induction  Top. — A  top  consisting  of  an  iron  disc  sup- 
ported on  a  vertical  axis,  which,  when  spun  before  the  poles 
of  a  steel  magnet  assumes  an  inclined  position,  through  the 
influence  of  the  currents  induced  in  the  disc. 

The  top  maintains  the  inclined  position  so  long  only  as  the 
strength  of  the  induced  currents  is  sufficiently  great ;  that  is 
while  speed  of  rotation  is  sufficiently  great. 

Induction,  Tubes  of (See  Force,  Tubes  of,  or 

Tubes  of  Induction. ) 

Inductive  Capacity,  Specific (See  Capac- 
ity, Specific  Inductive.) 

Iiiductomctcr,  Differential An  appa- 
ratus for  measuring  by  means  of  a  galvanometer  the  momen- 
tary currents  produced  by  the  discharge  of  a  cable. 

Currents  produced  by  the  discharge  of  a  cable  are  of  so 
short  a  duration  that  they  do  not  produce  much  effect  on  a 
galvanometer  needle. 

The  inductive  charge  in  a  cable,  or  the  quantity  of  elec- 
tricity produced  in  it  by  induction,  is 

(1)  Directly  as  the  electromotive  force  of  the  charging  bat- 
tery. 

(2)  Inversely  as  the  square  root   of  the   thickness  of  the 
coating  of  gutta-percha  or  other  insulating  material  between 
the  conducting  wires  and  the  metallic  sheathing,  and 

(3)  Directly  as  the  square  root  of  the  diameter  of  the  copper 
wire  of  the  conductor.     In  order  to  cause  the  cable  discharge 
to  more  thoroughly  affect   the    galvanometer  needle,   Mr. 


844  A  DICTIONARY  OF  ELECTRICAL 

Latimer  Clark  employed  a  differential  instrument  with  a  large 
battery,  and  three  reversing  keys,  by  means  of  which  he  gave 
a  rapid  successsion  of  charges  to  the  cable.  He  called  the 
instrument  a  Differential  Inductometer. 

Inductophone. — A  device  suggested  by  Mr.  Willoughby 
Smith  for  obtaining  electric  communication  between  trains  in 
motion  and  fixed  stations  by  means  of  the  induction  currents 
developed  in  a  spiral  of  wire  fixed  on  the  moving  engine,  in 
its  motion  past  spirals  on  the  line,  into  which  intermittent 
currents  are  passed. 

.  The  spiral  on -the  engine  is  placed  in  the  circuit  of  a  tele- 
phone. (See  Telegraphy,  Inductive.) 

Inductorium.— A  name  sometimes  applied  to  a  Ruhm- 
korff  induction  coil.  (See  Induction  Coils.) 

Inertia. — The  inability  of  a  body  to  change  its  condition 
of  rest  or  motion,  unless  some  force  acts  on  it. 

The  inertia  of  matter  is  expressed  in  Newton's  first  law  of 
motion,  as  follows  : 

"  Every  body  tends  to  preserve  its  state  of  rest  or  of  uniform 
motion  in  a  straight  line,  unless  in  so  far  as  it  is  acted  on  by 
an  impressed  force." 

All  matter  possesses  inertia. 

Inertia,  Magnetic or  Lag.— The  inability  of  a 

magnet  core  to  instantly  lose  or  acquire  magnetism. 

The  magnet  core  tends  to  continue  in  the  magnetic  state  in 
which  it  was  last  placed. 

To  decrease  the  magnetic  inertia  the  strength  of  the  mag- 
netizing current  is  increased  and  the  length  of  the  iron  core 
decreased.  The  iron  should  also  be  quite  soft.  (See  Coercive 
Force.  Lag,  Magnetic.) 

Infinity  Plug.— A  plug,  in  a  box  of  resistance  coils,  in 
which  the  two  pieces  of  brass  it  connects  are  not  connected  by 
any  resistance  coil  and  which,  therefore,  leaves  on  unplugging, 
an  open  circuit  or  an  infinite  resistance. 


WORDS,  TERMS  AND  PHRASES.  345 

Ink- Writer,  Telegraphic,  —  —  or  Recorder. 

(See  Balance,  Wheatstone's  Electric,  Box,  Form  of.) — A  de- 
vice employed  for  recording  the  dots  and  dashes  of  a  tele- 
graphic message  in  ink  on  a  fillet  or  strip  of  paper. 

Insolation,  Electric.— (See  Sun  Stroke,  Electric.) 

Installation. — A  term  embracing  the  entire  electric  plant 
and  its  accessories  required  to  perform  any  specified  work. 

Insulating  Cements. — (See  Cements,  Insulating.) 

Insulating  Materials.— Non-conducting  substances 
which  surround  a  conductor,  in  order  that  it  may  either  retain 
an  electric  charge,  or  permit  the  passage  of  an  electric  current 
through  the  conductor  without  sensible  leakage. 

Various  gases,  liquids,  or  solids  may  be  employed  as  insu- 
lators. A  high  vacuum  affords  the  best  known  insulation. 

Insulating  Stool. — A  stool  provided  with  insulating 
legs,  on  which  a  person,  or  other  body,  may  be  placed  in  order 
to  receive  an  electric  charge. 

Insulating  Tape.— (See  Tape,  Insulating.) 
Insulating  Varnish. — (See  Varnish,  Insulating.) 

Insulators,  Telegraphic  or  Telephonic. 

Non-conducting  supports,  by  means  of  which  telegraphic, 
telephonic,  electric  light  wires,  or  other  wires  are  attached 
to  the  objects  by  which  they  are  supported. 

The  insulators  are  g-enerally  made  of  glass,  earthenware, 
porcelain,  or  hard  rubber,  and  assume  a  variety  of  forms, 
some  of  which  are  shown  in  Figs.  246,  247,  and  248.  Of  what- 
ever material  they  are  made,  it  is  necessary  that  the  surface 
on  which  the  wire  rests,  or  around  which  it  is  wrapped, 
should  be  smooth  so  as  to  avoid  abrasion  either  of  its  insulat- 
ing covering  or  of  the  wire  itself. 

Two  things  are  to  be  considered  in  the  selection  of  an  insu- 
lator, viz.  : 


346  A  DICTIONARY  OP  ELECTRICAL 

(1)  The  insulating-  power  of  the  material  of  which  it  is  com- 
posed, so  as  to  reduce  the  leakage  as  much 
as  possible.     (See  Electric  Leakage).     And, 
(2)  The  tensile  strength  of  the  material, 
so  that  in  case  of  heavy  wires  no  breaks 
may  result  from  the  fracture  of  the  insulator. 
Intensify  of  Current.— A  term  some- 
times employed  to  indicate  current  strength. 
(gee  Ampere.) 

Intensity  of  Field. — The  strength  of  a  field  as  meas- 
ured by  the  number  of  lines   of   force 
that  pass  through  it  per  unit  of  area  of 
cross  section.     (See  Field,  Electrostatic. 
Field,  Magnetic.) 

Intensity  of  Light.— The  brilliancy 
or  illuminating  power  of  a  light  as 
measured  by  a  photometer  in  standard 
candles.  (See  Photometer.) 

Intensity  of  magnetization,  or 
magnetic  Density.— The  strength  of  Fig. 

magnetism  as  measured  by  the  number  of  lines  of  magnetic 
force  that  pass  through  a  unit  of  area  of  cross 
section  of  the  magnet,  i.  e.,  a  section  taken  at 
right  angles  to  the  lines  of  force.  (See  Magnetic 
Density.) 

Interlocking  Apparatus. — Devices  for  me- 
chanically operating  railroad  switches,  and  sema- 
phore signals  for  indicating  the  position  of  such 
switches,  from  a  distant  signal  tower,  by  means 
of  a  system  of  interlocking  levers,  so  constructed 
that  the  signals  and  the  switches  are  interlocked, 
so  as  to  render  it  impossible,  after  a  route  has 
once  been  set  up  and  a  signal  given,  to  clear  a 
signal  for  a  route  that  would  conflict  with  the  one  previously 
setup. 


WORDS,  TERMS  AND  PHRASES.  347 

Intermittent  Earth.— (See  Earths.) 
Interrupter. — Any  device  for  interrupting  or  breaking  a 
circuit. 

Interrupter,  Automatic (See  Automatic  Con- 
tact Breaker.} 

Interrupter,  Tuning;  Fork  or  Reed  — 
An  interrupter  in  which  the  makes  and  breaks  are  caused  to 
follow  one  another  by  the  vibrations  of  a  tuning  fork  or  reed. 
The  tuning  fork  or  reed  is  maintained  in  vibration  by  any 
suitable  means.  Such  interrupters  are  applied  to  various 
uses.  Synchronous  multiplex  telegraphy  is  an  example  of 
such  uses. 

Inverted  Induction  Coils.— (See  Converters  or  Trans- 
formers.} 

Ions. — Groups  of  atoms  or  radicals  which  result  from  the 
electrolytic  decomposition  of  a  molecule. 

The  ions  are  respectively  electro-positive  and  electro-ne- 
gative. The  electro-positive»  ion  appears  at  the  plate  con- 
nected with  the  electro  negative  terminal,  or  at  the  kathode, 
and  is  called  the  kathion. 

The  electro-negative  ion  appears  at  the  plate  connected 
with  the  electro-positive  terminal,  or  at  the  anode,  and  is 
called  the  anion.  (See  Electrolysis.  Kathion.  Anion.) 

Iron-Clad  Magnet. — A  magnet  in  which  the  magnetic 
resistance  is  lowered  by  a  casing  of  iron  connected  with  the 
core  and  provided  for  the  passage  of  the  lines  of  magnetic 
force.  (See  Magnet,  Tubular.) 

Isobar*,  or  Isobarie  Lines.— Lines  connecting  places 
on  the  earth's  surface  which  have  at  any  time  the  same 
barometric  pressure. 

A  study  of  the  isobaric  lines,  or  isobars,  is  of  great  assist- 
ance in  making  forecasts  or  predictions  of  coming  changes  in 
the  weather. 

Isochronism.— Equality  of  time  of  vibration. 


348  A  DICTIONARY  OF  ELECTRICAL 

Isochronous  Vibration*  or  Oscillations.— Vibra- 
tions which  perform  their  to  and  fro  motions  on  either  side  of 
the  position  of  rest  in  equal  times. 

The  vibrations  of  a  pendulum  are  isochronous,  no  matter 
what  the  amplitude  of  the  swing  may  be,  that  is.  whether  the 
pendulum  swings  through  a  large  arc  or  a  small  arc,  provided 
this  arc  be  not  very  great.  All  vibrations,  therefore,  that 
produce  musical  sounds  may  be  regarded  as  isochronous. 

Isoclinic  Charts. — (See  Inclination  Map  or  Charts.) 

Isoclinic  litnes.— Lines  connecting  places  that  have  the 
same  angle  of  magnetic  dip  or  inclination.  (See  Dip,  Mag- 
netic.) 

Isodynamic  Lines. — Lines  connecting  places  which  have 
the  same  magnetic  intensity. 

The  magnetic  intensity  of  a  place  is  determined  by  the 
number  of  oscillations  that  a  small  magnetic  needle,  moved 
from  its  position  of  rest  in  the  magnetic  meridian  of  any 
place,  makes  in  a  given  time.  This  method  is  similar  to  that 
employed  for  determining  the  intensity  of  gravity  at  any 
place  by  observing  the  number  of  oscillations  that  a  pen- 
dulum of  a  given  length  makes  in  a  given  time  at  that  place. 
If,  for  example,  a  magnetic  needle  at  one  place  makes  211  os- 
cillations in  ten  minutes,  and  245  in  the  same  time  at  another 
place,  the  relative  magnetic  intensities  at  these  places  are  as 
the  squares  of  these  numbers  or  as  44521 :  60025,  or  as  1 :  1.348. 

Isodynamic  Map  or  Chart  — A  map  of  the  earth  on  a 
Mercator's  projection  on  which  isodynamic  lines  are  drawn. 

An  isodynamic  chart  is  shown  in  Fig.  249.  It  will  be  ob- 
served that  the  isodynamic  lines  do  not  exactly  coincide  with 
the  isoclinic  lines,  since  the  line  of  least  magnetic  intensity, 
does  not  correspond  with  the  line  of  the  magnetic  equator. 

The  point  of  least  magnetic  intensity  is  found  at  about  lat. 
20°  S,  and  long.  35°  W.  The  point  of  greatest  magnetic  in- 
tensity, is  found  at  about  lat.  52°  N.  and  long.  92°  W. 


WORDS,  TERAIS  AND  PHRASES. 


349 


350  A   MUTIONAKY    OF   ELKOTKKJAt, 

Another  though  weaker  point  of  great  magnetic  intensity 
is  found  in  Siberia.  These  are  distinguished  from  the  true 
magnetic  poles  by  the  term  Poles  of  Intensity. 

The  Poles  of  Verticity,  as  determined  by  the  dipping  needle, 
and  the  poles  t  intensity  as  determined  by  the  needle  of  os- 
cillation, therefore  do  not  coincide  in  the  northern  hemisphere. 

Isogonal  Lines. — Lines  connecting  places  that  have  the 
same  magnetic  variation  or  declination.  (See  Declination, 
Magnetic.) 

Isogonic  or  declination  Hap  or  Chart.— A  chart 
on  which  the  isogonal  lines  are  marked. 

In  the  declination  or  variation  chart,  shown  in  Fig.  250,  the 
region  of  western  declination  is  indicated  by  the  shading. 
There  is  a  remarkable  oval  patch  in  the  northeastern  part  of 
Asia,  in  which  the  declination  is  west.  A  similar  oval  of  de- 
creased declination  is  seen  in  the  southern  Pacific. 

The  entire  earth  acts  as  a  huge  magnet  with  an  excess  of 
south  magnetic  polarity  in  the  northern  hemisphere. 

It  is  not  known  whether  the  earth  possesses  more  than 
a  single  pair  of  magnetic  poles,  or  what  is  the  exact  cause 
of  its  magnetism.  The  variations  in  the  declination,  and 
in  the  intensity  of  its  magnetism,  due  to  the  position  of 
the  sun,  as  well  as  the  marked  magnetic  disturbances  that 
accompany  the  occurrence  of  sun  spots,  would  appear  to  con- 
nect the  earth's  magnetism  with  the  solar  radiation. 

It  is  believed  by  some  that  the  earth  possesses  in  reality 
the  two  magnetic  poles,  viz.,  a  south  pole  in  the  northern 
hemisphere,  and  a  north  pole  in  the  southern  hemisphere. 
(See  False  Poles,  Magnetic.) 

Isotropic  Conductor. — A  conductor  which  possesses  the 
same  powers  of  electric  conduction  in  all  directions. 

An  electrically  homogeneous  medium. 

Isotropic  Medium. — A  transparent  medium  which  pos- 
sesses the  same  optical  or  electric  properties  in  all  directions. 

An  optically  homogeneous,  transparent  medium. 


WORDS,  TERMS  AND  PHRASES. 


A  DICTIONARY  OF  ELECTRICAL 


An  electrically  isotropic  medium  possesses  the  same  pow  ers 
of  electric  conduction  or  spe- 
cific inductive  capacity  in  all 
directions.  (See  Anistropic 
Medium,.') 

I.  W.   G.— A   contraction 
for  Indian  Wire  Gauge. 

Jar,  Leyden A 


condenser  in  the  form  of  a  jar, 
in  which  the  metallic  coatings 
are  placed  opposite  to  each 
other  on  the  outside  and  the 
inside  of  the  jar. 

The  metal  coatings  should 
not  extend  to  more  than  two- 
Mff-  251-  thirds  the  height  of  the  jar, 

the  rest  of  the  glass  being  varnished  to  avoid  the  creeping  of 
the  charge  over  the  glass  in  damp  weather.       a  ( 
The  inside  coating  is  connected  by  means 
of  a  metallic  chain,  to  a  rounded  knob  on 
the  top  of  the  jar,  as  shown  in  Fig.  251. 
The  conductor  supporting  the  knob  passes 
through  a  dry  cork  or  plug  of  some  insulat- 
ing material. 

To  charge  the  jar  the  outside  coating  is 
connected  with  the  earth,  as  by  holding  it 
in  the  hand,  and  the  inside  coating  is  con- 
nected with  the  conductor  of  a  machine. 

Jar,  Unit A  small  Leyden  jar 

sometimes  employed  to  measure  approxi- 
mately the  quantity  of  electricity  passed 
into  a  Leyden  battery  or  condenser. 

As  shown  in  Fig.  252,  the  unit  jar  consists  of  a  small  Leyden 
jary,  whose  outer  coating  is  connected  with  a  sliding  metallic 


WORDS,  TERMS  AND  PHRASES.  353 

rod  6,  provided  at  each  end  with  a  rounded  knob,  and  the  inner 
coating  of  which  is  connected  with  a  metallic  knob  c,  placed, 
and  as  shown,  inside  a  glass  jar  d,  opposite  the  ball  on  the 
long  end  of  b. 

When  now  the  inside  of  the  unit  jar,  or  the  end  connected 
with  c,  is  connected  with  the  charging  source,  such  as  a 
machine,  and  the  outside  at  a  is  connected  with  the  battery 
that  is  to  be  charged,  for  every  spark  that  passess  between 
d  and  c,  a  definite  quantity  has  passed  at  a. 

The  value  of  this  unit  charge,  may  be  varied  by  varying  the 
distance  between  d  and  c. 

The  smaller  the  unit  jar  in  proportion  to  the  jar  to  be 
charged,  and  the  shorter  the  distance  between  c  and  d,  the 
more  reliable  are  the  comparative  results  obtained. 

Jet  Photometer.  —  An  apparatus  for  determining  the 
candle  power  of  a  luminous  source.  (See  Carcel,  Standard.) 

Jewelry,  Electric  --  The  substitution  of  minute 
incandescent  electric  lamps  for  the  rarer  gems  in  articles  of 
jewelry. 

The  lamps  are  lighted  by  means  of  small,  primary  storage 
batteries,  carried  in  the  pocket 

Joint  Resistance  of  Parallel  Circuits.—  The  joint 
resistance  of  two  parallel  circuits  is  determined  by  means  of 
the  following  formula  : 


R 
~ 


Where  R  =  the  joint  resistance  of  any  two  circuits  whose 
separate  resistances  are  respectively  r  and  r'. 

When  there  are  three  resistances  r,  r'  and  r",  in  parallel, 
the  joint  resistance, 

rr'r" 


R=- 


(See  Circuits,  Varieties  of.) 


354  A  DICTIONARY  OF  ELECTRICAL 

Joint  Testing.— Ascertaining  the  resistance  of  the  in- 
sulating material  around  the  joint  in  a  cable. 

The  resistance  of  a  cable  at  its  joint  is  necessarily  high, 
since  the  joint  forms  but  a  small  part  of  length  of  the  cable. 
It  should  not,  however,  be  large  as  compared  with  an  equal 
length  of  another  part  of  the  cable  with  a  perfect  core. 

Two  methods  for  the  testing  of  cable  joints  are  generally 
employed,  viz.: 

(1)  A  condenser  is  charged  through  the  joint  for  a  given 
time,  and  the  deflection  obtained  by  its  discharge  is  compared 
with  the  discharge  of  the  same  condenser  charged  for  an 
equal  length  of  time  through  a  few  feet  of  perfect  cable. 

(2)  A  charged  condenser  is  permitted  to  discharge  itself 
through  the  joint,  and  the  amount  lost  after  a  given  time 
noted. 

For  description  of  methods,  see  Kempe's  "Handbook  of 
Electrical  Testing." 

Joints,  Butt End  to  end  joints. 

Butt  joints  are  formed  by  bringing  the  ends  to  be  joined 
together  and  securing  them  while  in  such  position. 

Joints,  Butt  and  Lap for  Wires.— Joints 

effected  in  wires  either  by  placing-  the  wires  end  on,  or  by 
overlapping  the  ends,  and  subsequently  soldering. 

Joints,  Butt  and  Lap of  Beits.— The  joints  in  a 

leather  belt,  employed  for  transmitting  power  from  a  line  of 
shafting,  where  the  ends  are  simply  brought  together  and 
laced,  is  called  &butt  joint,  in  contradistinction  to  a  lap  joint, 
or  a  joint  formed  by  placing  one  end  of  the  belt  over  the  other 
and  lacing  or  riveting  the  two. 

In  delicate  galvanometers  the  slightest  change  in  the  speed 
of  the  engine  driving  the  dynamo-electric  machine  producing 
the  current,  causes  an  annoying  fluctuation  of  the  needle  that 
prevents  accurate  reading,  when  lap  joints  are  used  in  the 
belt  instead  of  butt  joints,  unless  the  former  are  very  carefully 
made.  It  also  causes  a  flickering  in  the  lights, 


WORDS,  TERMS  AND  PHRASES.  355 

Joints,  Expansion Joints  for  underground  con- 
ductors, tubes  or  pipes,  exposed  to  considerable  changes  of 
temperature,  in  which  a  sliding  joint  is  provided  to  safely 
permit  a  change  of  length  on  expansion  or  contraction. 

Joints,  L.ap Joints  effected  by  overlapping  short 

portions  near  the  ends  of  the  two  things  to  be  joined,  and  secur- 
ing them  while  in  such  position. 

Joints,     Telegraphic,    Telephonic,    etc. 

Methods  adopted  for  joining  the  ends  of  electric  conductors  so 
as  to  insure  a  permanent  junction  whose  resistance  shall  not 
be  appreciably  greater  per  unit  of  length  than  that  of  the  rest 
of  the  wire. 

In  making  a  joint  care  should  always  be  taken  to  clean  and 
scrape  the  insulating  material  from  the  wires  before  twisting 
them  together. 

Telegraph  wires  were  formerly  joined  by  the  ordinary  bell- 
hanger's  joint ;  that  is,  the  wires  were  simply  looped  together. 
The  constant  vibrations  to  which  the  wires  are  subject  caused 
such  a  joint  to  be  abandoned  and  an  improvement  introduced 
by  bolting  the  ends  together,  as  shown  in  Fig.  253. 

This  latter  method  is  now  replaced  by  the  following,  viz.: 

In  the  Britannia  Joint,  shown  in  Fig.  254,  the  wires  to  be 
joined  are  placed  side  by  side  for  about  two  inches,  bound 
with  No.  16  (British  gauge)  binding  wire,  in  the  manner 
shown,  and  then  carefully  soldered. 

The  American  Twist  Joint,  shown  in  Fig.  255,  is  made  by 
twisting  the  wires  together  in  the  manner  shown  and  sub- 
sequently soldering. 

This  joint  is  easily  made  and  is  quite  serviceable. 

All  joints  should  be  soldered,  but  in  so  doing  care  must  be 
taken  that  the  soldering  liquid  or  solid  employed  is  free  from 
acids  or  other  corrosive  materials,  and  that  ail  traces  of  such 
materials  are  removed  before  the  joint  is  covered  with  insulat- 
ing material. 


356 


A  DICTIONARY  OF  ELECTRICAL 


Kerite,  Okonite,  or  other  insulating  Tape,  should  preferably 
be  wrapped  around  the  joint  after  it  is  soldered. 

In  making  a  joint  in  a  gutta-percha  covered  wire,  such  as 
a  submarine  cable  wire,  or  wires,  the  following  method 
may  be  employed :  The  bared  and  cleansed  wires  are 


fig.  253. 

twisted  together  and  soldered.  The  soldered  joint  is  then 
covered  with  a  layer  of  plastic  insulating  material  made  of  a 
mixture  of  gutta-percha,  tar  and  rosin.  (See  Chattertori's 
Compound.)  In  order  to  insure  a  good  junction  between  this 
and  the  gutta-percha  covering  on  the  rest  of  the  wire,  the 


ZEE 


fig.  25k. 

outer  surface  of  the  gutta-percha  is  removed  for  about  two 
inches  from  each  side  of  the  joint  so  as  to  remove  its 
oxidized  surface.  After  the  coating  is  put  on,  it  is  warmed 
gently  by  a  warm  joining  tool  and  not  by  the  flame  of  a  lamp. 
A  sheet  of  warmed  gutta-percha  is  then  wrapped  around  the 


fig.  S55. 

joint,  and  while  it  and  the  joint  are  still  hot,  another  coating 
of  the  plastic,  insulating  material  is  applied.  Successive 
layers  of  gutta-percha  and  insulating  material  are  generally 
applied  in  the  case  of  submarine  cables.  (Culley.) 

Joulad.— A  term  proposed  for  the  Joule,  but  not  genei'- 
ally  adopted.    (See  Joule.) 


WORDS,  TERMS  AND  PARASES.  35? 

Joule. — The  unit  of  electric  energy  or  work. 
The  volt-coulomb. 

The  amount  of  electric  work  required  to  raise  the  potential 
of  one  coulomb  of  electricity  one  volt 

The  joule  may  be  regarded  as  a  unit  of  work  or  energy  in 
general,  apart  from  electrical  work  or  energy. 

1  joule. =  10,000,000  ergs. 

1  joule. =  .73732  foot  pound. 

1  joule —  1  volt-coulomb. 

4.2  joules =  1  small  calorie. 

1  joule  per  second =  1  watt. 

The  British  Association  recently  proposed  to  call  one  joule 
the  work  done  by  one  watt  per  second. 

Joule  Effect.— The  heating  effect  produced  by  the 
passage  of  an  electric  current  through  a  conductor,  arising 
merely  from  the  resistance  of  the  conductor.  (See  Effect, 
Joule.) 

Kaolin.— A  variety  of  white  clay  sometimes  employed  for 
insulating  purposes. 

Jablochkoff  employed  kaolin  between  the  parallel  carbons 
of  his  electric  candle  for  the  purpose  of  insulating  them.  He 
also  devised  an  electric  lamp  in  which  a  spark  of  considerable 
difference  of  potential,  obtained  from  an  ordinary  induction 
coil,  was  caused  to  raise  a  surface  of  kaolin  to  incandescence 
by  its  passage  over  it. 

Katheleetrotonus,  or  Kateleetrotonus.— In  elec- 
tro therapeutics  the  condition  of  increased  functional  activity 
that  occurs  in  a  nerve  in  the  neighborhood  of  the  negative 
electrode,  or  the  kathode  applied  in  medical  electricity.  (See 
Electrotonus.) 

Katllioii.— The  electro  positive  ion,  atom,  or  radical  into 
which  the  molecule  of  an  electrolyte  is  decomposed  by  electro- 
lysis. (See  Electrolysis.  Ions.) 

Kathion  is  sometimes  improperly  written  cation. 


358 


A  DICTIONARY  OF  ELECTRlCAl. 


Kathode.  —  The  conductor  or  plate  of  a  decomposition  cell 
connected  with  the  negative  terminal  or  electrode  of  a  battery 
or  other  source. 

The  word  kathode  is  sometimes  applied  to  the  negative 
terminal  of  a  battery  or  source,  whether  connected  with  a 
decomposition  cell  or  not.  It  is  preferable,  however,  to 
restrict  its  use  to  a  decomposition  cell.  (See  Anode.) 

The  word  kathode  is  often  improperly  written  cathode. 


Fig.  356. 

Kathodic  and  Anodic  Electro-Diagnostic  Re- 
actions.— The  reactions  which  occur  at  the  kathode  or  anode 
of  an  electric  source  placed  on  or  over  any  part  of  a  living- 
body. 

Fig.  256,  from  DeWatteville's  Medical  Electricity,  represents 
what  he  assumes  takes  place  at  the  points  of  entrance  and 
exit  of  the  current  in  a  nerve  submitted  to  the  action  of  the 
anode  of  an  electric  source.  Two  zones  are  formed,  an  anodic 
and  kathodic;  the  virtual  anode  is  formed  by  the  portion  of  the 
skin  nearer  the  nerve,  and  the  virtual  kathode  in  the  adjoin- 
ing muscles.  There  are  thus  formed  two  zones  of  influence, 


WORDS,  TERMS  AND  PHRASES.  359 

One,  immediately  around  the  anode,  called  the  polar,  or  anelec- 
trotonic  zone,  and  one,  surrounding1  this  and  including1  the 
virtual  kathode,  and  called  the  peripolar,  or  katelectrotonic 
zone. 

K.  C.  C. — In  electro  therapeutics,  a  brief  method  of  writing 
kathodic  closure  contraction,  or  the  effects  of  muscular  con- 
traction observed  by  the  closure  of  a  circuit  at  the  kathode. 

K.  D.  C.— In  electro  therapeutics,  a  brief  method  of  writing 
kathodic  duration  contraction,  or  the  effects  of  muscular  con- 
traction observed  at  the  kathode  after  the  current  has  been 
passing  for  some  time. 

Keeper  of  Magnet.— A  mass  of  soft  iron  applied  to  the 
poles  of  a  magnet  through  which  its  lines  of  magnetic  force 
pass.  (See  Field,  Magnetic.) 

The  keeper  of  a  magnet  differs  from  its  armature  in  that 
the  keeper  while  acting  as  such  is  always  kept  on  the  poles  to 
prevent  loss  of  magnetization  while  the  armature,  besides  act- 
ing as  a  keeper,  may  be  attracted  towards,  or  repelled  from, 
the  magnet  poles.  While  performing  its  functions  the  keeper 
is  always  fixed;  the  armature  generally,  though  not  always,  is 
in  motion. 

Opinion  is  divided,  however,  on  the  efficacy  of  the  keeper. 

Key-Board.— (See  Board,  Switch.) 

Key,  Discharge. — A  key  employed  to  enable  the  dis- 
charge from  a  condenser  to  be  readily  passed  through  a 
galvanometer  for  purposes  of  measurement. 

Key,  Discharge,  Kempe's A  discharge  key 

constructed  as  shown  in  Fig.  257. 

The  solid  lever,  hinged  at  one  extremity,  plays  between  two 
contacts  connected  to  two  terminals,  and  has  two  finger  triggers 
at  its  free  end  marked  "Discharge"  and  "Insulate,"  con- 
nected to  two  ebonite  hooks  respectively.  The  hook  at- 
tached to  that  marked  "Discharge"  is  a  little  higher  than 
the  other,  so  that  when  the  lever  is  caught  against  it,  the 


360  A  DICTIONARY  OP  ELECTRICAL 

key  rests  in  an  intermediate  position  between  the  two  con- 
tacts, and  when  caught  against  the  lower  trigger,  it  rests 
against  the  bottom  contact.  When  in  the  last  position,  a  de- 
pression of  the  "Insulate"  trigger  causes  the  lever  to  spring 
up  against  the  second  hook,  thus  insulating  it  from  either  con- 
tact, and  on  the  depression  of  the  "Discharge"  trigger,  the 
lever  springs  up  against  the  top  contact. 


Fig.  257. 

Key,  Discharge,  Webb's A  discharge  key  con- 
structed as  shown  in  Fig.  258. 

A  horizontal  lever  L,  Fig.  258,  passing  between  two  contacts 
and  hinged  at  J,  is  pressed  upwards  by  a  spring.  The  free  end 
of  this  lever  terminates  in  two  steps  1  and  2.  A  vertical  lever 
H,  provided  with  an  insulating  handle,  is  jointed  at  J',  and  has, 
at  C  a  projecting  metallic  tongue  that  engages  in  the  upper 
step  when  the  lever  H,  is  vertical,  and  on  the  lower  step  when 
it  is  slightly  moved  from  the  free  end. 

When  the  projection  C  rests  on  the  lower  step  2,  the  lever 
L  is  intermediate  between  the  top  and  bottom  contacts,  and  is 
therefore  disconnected  from  either  of  them  ;  but,  when  it  rests 
on  the  upper  step,  it  is  in  contact  with  the  lower  contact. 
When  the  lever  H  is  so  moved  as  to  have  the  projection  C, 
away  from  both  contacts,  the  lever  L  is  pressed  by  its  spring 
against  the  upper  contact. 


WORDS,  TERMS  AND  PHRASES. 


The  battery  terminals  are  connected  with  the  condenser 
terminals  when  the  lever  L,  is  touching  the  lower  contact,  but 
when  the  lever  L,  touches  the  top  contact,  the  condenser  is 
connected  with  the  galvanometer  terminals. 


If 


Fig.  258. 

Key,    Double-Contact     Form    of    Bridge    Key, 

Sprague's — A  key  designed  to  close  two  separate 

circuits  successively. 

On  depressing  K, 
Fig.  259,  the  contacts 
c,  c,  are  first  closed 
and  then  those  at  c',  c'. 
Metallic  pieces  1,  2,  3 
and  4,  serve  to  make 
contacts  with  appar- 
atus used  in  connec- 
tion therewith. 

The  battery  circuit 
is  connected  to  1  and 
2,  and  the  galvanome-  F*ff- S59- 

ter  to  3  and  4,  so  that  the  battery  circuit  is  closed  first,  and 
the  galvanometer  afterwards.  Used  in  connection  with  the 
Wheatstone  Bridge. 


A  DICTIONARY  OP  ELECTRICAL 


Key,  Double-Contact 


-,  Lambert's.— A  key  used 


in  cable  work,  and  constructed  as  shown  in  Fig.  260. 
F 


In  Thomson's  method  for  the  determination  of  electrostatic 
capacity,  the  capacity  of  the  cable  is  compared  with  that  of  a 
condenser  containing  a  known  charge.  These  two  charges  are 
so  connected  electrically  as  to  discharge  into  and  neutralize 

each  other  if  equal, but  if 
not,  to  produce  a  gal- 
vanometer deflection  by 
a  charge  equal  to  their 
difference. 

The  connections  are 
such  that  the  pushing 
forward  of  K,  depresses 
keys  that  permit  a  bat- 
tery to  simultaneously  charge  the  condenser  and  the  cable. 
On  drawing  K,  back,  the  difference  of  the  two  charges  are 
allowed  to  mix.  Then,  on  depressing  k,  the  difference  of  the 
charge,  if  any,  is  discharged  through  the  galvanometer. 

Hey,  Magneto-Electric A  telegraph  key  for 

sending  an  electric  impulse  into  a  line,  so  arranged  that  the 


WORDS,  TERMS  AND  PHRASES.  363 

coil  of  wire  on  an  armature  connected  with  the  key  lever, 
is,  by  the  movements  of  the  key,  moved  towards  or  from 
the  poles  of  a  permanent  magnet,  the  movements  of  the  key 
thus  producing  the  currents  sent  into  the  line. 

Key,  Plug A  simple  form  of  key  in  which  a  con- 
nection is  readily  made  or  broken  by  the  insertion  of  a  plug 
of  metal  between  two  metallic  plates  that  are  thus  introduced 
into  a  circuit. 

A  form  of  plug-key  is  shown  in  Fig.  261. 

Key,  Reversing A  key,  inserted  in  the  circuit 

of  a  galvanometer  for  obtain- 
ing deflections  of  the  needle 
on  either  side  of  the  galvano- 
meter scale. 

The  galvanometer  termin- 
als are  connected  to  the  bind- 
ing posts  2  and  3,  Fig.  262, 
and  the  circuit  terminals  to 
the  other  two  posts.  On  de- 
pressing K,  the  current  flows 
in  one  direction  and  on  de-  Fiff'  2S2' 

pressing  K',  in  the  opposite  direction.  Clamps,  operated  by 
handles,  are  provided  so  as  to  close  either  of  the  keys  per- 
manently, if  so  desired. 

Key,  Short-Cireuit  —  —A  key,  which  in  its  normal 
condition  short-circuits  the  galvanometer. 

Such  a  short-circuit  key  is  provided  for  the  purpose  of  pro- 
tecting the  gavanometer  from  injury  by  large  currents  being 
accidentally  passed  through  its  coils.  In  the  form  shown  in 
Fig.  263,  the  spring  S,  rests  against  a  platinum  contact,  but 
when  depressed  by  the  insulated  head  at  K,  it  rests  against 
an  ebonite  contact,  and  throws  the  galvanometer  into  the  de- 
sired circuit. 

The  key  is  provided  with  double  binding  posts  at  P  and  N, 


864 


A  DICTIONARY  OF  ELECTRICAL 


for  convenience  of    attachment    to    resistance  coils,  batter- 
ies, etc. 

In  the  form  of  short-circuit  key  shown  in  Fig.  264  a  catch  is 
provided  for  the  purpose  of  keeping  the  key  down  when  once 
depressed.  Its  arrangement  will  be  understood  from  an 
inspection  of  the  figure. 


Fiq,  S6S. 

Key,  Sliding-Contact The  key  employed  in  the 

slide  form  of  Wheatstone's  bridge,  to  make  contact  with 
the  wire  over  which  the  sliding  contact  passes.  (See  Balance, 
Wheatstone's,  Slide  Form  of.) 


Fig.  S6k. 

Key,  Telegraphic The  key  employed  for  send- 
ing over  the  line  the  successive  makes  and  breaks  that  pro- 
duce the  dots  and  dashes  of  the  Morse  alphabet,  or  the 
deflections  of  the  needle  of  the  needle  telegraph.  (See  Tele- 
graphy, American  or  Morse  System  of.) 


WORDS,  TERMS  AND  PHRASES.  365 

Kilo  (as  a  prefix). — One  thousand  times. 
Kilodyiic. — One  thousand  dynes.     (See  Dyne.) 

Kilogramme.— One  thousand  grammes,  or  2.2046  Ibs.  av- 
oirdupois. (See  Weights,  French  System,  of.) 

Kilojoule.— One  thousand  joules. 
Kilometre.— One  thousand  metres. 
Kilowatt.— One  thousand  watts. 

Kinc. — A  unit  of  velocity  proposed  by  the  British  Asso- 
ciation. 

A  kine  equals  one  centimetre  per  second. 

Kinetic  Energy. — Energy  which  is  actually  doing  work, 
as  distinguished  from  energy  that  only  possesses  the  power 
of  doing  work,  or  potential  energy.  (See  Energy.) 

Kite,  Franklin's A  kite  raised  in  Philadelphia, 

Pa.,  in  June,  1752,  by  means  of  which  Franklin  experiment- 
ally demonstrated  the  identity  between  lightning  and  elec- 
tricity, and  which,  therefore,  led  to  the  invention  of  the  light- 
ning rod. 

It  is  true  that  Dalibard,  on  the  10th  of  May,  1752,  prior  to 
Franklin's  experiment,  succeeded  in  drawing  sparks  from  a 
tall  iron  pole  he  had  erected  in  France.  This  experiment  was, 
however,  tried  at  the  suggestion  of  Franklin,  and  must  prop- 
erly be  ascribed  to  him. 

The  following  description  of  this  kite  is  given  by  Franklin 
in  the  following  letter  : 

Letter  XI.,  from  BENJ.  FRANKLIN,  Esq.,  of  Philadelphia,  to 
PETER  COLLINSON,  Esq.,  F.R.S.,  London. 

"OCT.  19,  1752. 

"As  frequent  mention  is  made  in  public  papers,  from  Europe, 
of  the  success  of  the  Philadelphia  experiment  for  drawing  the 
electric  fire  from  clouds  by  means  of  pointed  rods  of  iron 
erected  on  high  buildings,  etc.,  it  may  be  agreeable  to  the 


366  A  DICTIONARY  OF  ELECTRICAL 

curious  to  oe  informed  that  the  same  experiment  has  succeeded 
in  Philadelphia,  though  made  in  a  different  and  more  easy 
manner,  which  is  as  follows  : 

"  Make  a  small  cross,  of  two  light  strips  of  cedar,  the  arms 
so  long,  as  to  reach  to  the  four  corners  of  a  large  thin  hand- 
kerchief, when  extended  ;  tie  the  corners  of  the  handkerchief 
to  the  extremities  of  the  cross,  so  you  have  the  body  of  a  kite ; 
which,  being  properly  accommodated  with  a  tail,  loop,  and 
string,  will  rise  in  the  air,  like  those  made  of  paper  ;  but  this, 
being  of  silk,  is  fitter  to  bear  the  wet  and  wind  of  a  thunder 
gust  without  tearing.  To  the  top  of  the  upright  stick  of  the 
cross  is  to  be  fixed  a  very  sharp  pointed  wire,  rising  a  foot  or 
more  above  the  wood.  To  the  end  of  the  twine,  next  the 
hand,  is  to  be  tied  a  silk  ribbon,  and  where  the  silk  and  twine 
join,  a  key  may  be  fastened.  This  kite  is  to  be  raised  when  a 
thunder  gust  appears  to  be  coming  on,  and  the  person  who 
holds  the  string  must  stand  within  a  door  or  window,  or  under 
some  cover,  so  that  the  silk  ribbon  may  not  be  wet ;  and  care 
must  be  taken  that  the  twine  does  not  touch  the  frame  of  the 
door  or  window.  As  soon  as  any  of  the  thunder  clouds  come 
over  the  kite,  the  pointed  wire  will  draw  the  electric  fire  from 
them,  and  the  kite,  with  all  the  twine  will  be  electrified,  and 
the  loose  filaments  of  the  twine  will  stand  out  every  way, 
and  be  attracted  by  an  approaching  finger.  And  when  the 
rain  has  wet  the  kite  and  twine,  so  that  it  can  conduct  the 
electric  fire  freely,  you  will  find  it  stream  out  plentifully  from 
the  key  on  the  approach  of  your  knuckle.  At  this  key  the 
phial  may  be  charged ;  and  from  electric  fire,  thus  obtained, 
spirits  may  be  kindled,  and  all  the  other  electric  experiments 
be  performed,  which  are  usually  done  by  the  help  of  a  rub- 
bed glass  globe  or  tube,  and  thereby  the  sameness  of  the 
electric  matter  with  that  of  lightning  completely  demon- 
strated. B.  FRANKLIN." 

Kyanizing. — A  process  employed  for  the  preservation  of 
wooden  telegraph  poles  by  injecting  a  solution  of  corrosive 


WORDS,  TEEMS  AXD  PHRASES.  367 

sublimate  into  the  pores  of  the  wood.  (See  Poles,  Tele- 
graphic.') 

Lag,  magnetic The  tendency  of  the  iron  core  of 

a  magnet,  or  of  the  armature  of  a  dynamo-electric  machine,  to 
resist  and  therefore  retard  magnetization. 

This  retardation,  or  lag,  is  called  the  magnetic  lag. 

The  lead  necessary  to  give  the  brushes  of  a  dynamo-electric 
machine  to  ensure  quiet  action  has  by  some  been  erroneously 
ascribed  to  the  magnetic  lag.  The  lead,  though  due  to  lag  in 
part,  is,  in  reality,  mainly  due  to  the  resultant  magnetization 
of  the  armature  by  both  the  field  magnets  and  by  its  own  cur- 
rent. (See  Angle  of  Lead.) 

This  displacement  is  measured  by  an  angle  sometimes  called 
the  angle  of  lag  (See  Angle  of  Lag.) 

Lamination  of  Core.— The  subdivision  of  the  core  of 
the  armature  of  a  dynamo-electric  machine  into  separate  in- 
sulated plates  or  strips  for  the  purpose  of  avoiding  eddy  cur- 
rents. 

This  lamination  must  always  be  perpendicular  to  the  direc- 
tion of  the  eddy  currents  that  would  otherwise  be  produced. 
(See  Eddy  Currents). 

Lamellar  Distribution  of  Magnetism,  magnetic 
Shell. — The  distribution  of  magnetism  in  magnetic  shells. 

A  magnetic  shell  is  a  thin  sheet  or  disc  of  magnetized  mate- 
rial whose  opposite  extended  faces  are  of  opposite  magnetic 
polarities,  and  the  extent  of  whose  surface  is  very  great  as 
compared  with  its  thickness. 

The  field  produced  by  a  magnetic  shell  is  exactly  similar  to 
that  produced  by  a  closed  voltaic  circuit,  the  edges  of  the 
space  inclosed  by  which  correspond  to  the  edges  of  the  mag- 
netic shell. 

Magnetic  Density  or  Intensity,  or  the  number  of  lines  of 
force  per  unit  area  of  cross  section,  is  equal  over  all  parts  of 
the  surface  of  a  simple  magnetic  shell.  The  strength  of  such 


A  DICTIONARY  OF  ELECTRICAL 


a  shell  will  therefore  be  equal  to  its  thickness  multiplied  by 

its  surface  density. 
A  magnetic  shell  may  be  conceived  as  consisting  of  a  very 

great  number  of  exceedingly  short,  straight,  magnetic  needles 

placed  side  by  side,  with  their  north  poles  terminating  at  one 
of  the  faces  of  the  sheet  and  their  south 
poles  at  the  opposite  face,  the  breadth  of 
the  sheet  being  very  great  as  compared 
with  its  thickness.  Such  a  distribution  of 
magnetism  is  known  as  a  lamellar  dis- 
tribution. 


Lamp,  Arc,  Electric 


An 

electric  lamp  in  which  the  light  is  pro- 
duced by  a  voltaic  arc  formed  between  two 
or  more  carbon  electrodes. 

The  carbon  electrodes  are  placed  in 
various  positions,  either  parallel,  horizon- 
tal, inclined,  or  vertically  one  above  the 
other.  The  latter  is  the  form  most  gen- 
erally adopted,  since  it  permits  the  ready 
feeding  of  the  upper  carbon. 

The  carbons  are  maintained  during  their 
consumption,  at  a  constant  distance  apart, 
by  the  aid  of  various  feeding  devices. 
Such  devices  consist  generally  of  trains  of 
wheelwork,  mechanical  or  electric  motors, 
or  are  operated  by  the  simple  action  of  a 
spring,  gravity  or  a  solenoid. 

The  carbon  pencils  or  electrodes  are  held 
in  carbon  holders,  consisting  of  clutches 
or  clamps,  attached  to  the  ends  of  the  lamp  rods. 

When  the  lamp  is  not  in  operation  the  carbons  are  usually  in 
contact  with  one  another  ;  but,  on  the  passage  of  the  current, 
they  are  separated  the  required  distance  by  the  action  of  an 
electromagnet  whose  coils  are  traversed  by  the  direct  current. 


Fig.  265. 


WORDS,  TERMS  AND  PHRASES.  369 

In  order  to  maintain  the  electrodes  a  constant  distance 
apart,  the  upper  carbon  is  held  in  position  by  the  operation  of 
a  clutch  in  some  lamps,  or,  in  others,  by  a  detent,  that  en- 
gages in  a  toothed  wheel.  The  position  of  this  clutch  or  detent 
is  controlled  by  the  action  of  an  electro-magnet  whose  coils  are 
usually  situated  in  a  shunt  or  derived  circuit,  of  high  resis- 
tance, around  the  electrodes.  When  the  carbons  are  at  their 
normal  distance  apart,  the  shunt  current  is  not  of  sufficient 
strength  to  move  the  clutch  or  detent  from  the  position  in 
which  it  prevents  the  downward  motion  of  the  upper  carbon 
rod.  When,  however,  by  the  burning  or  consumption  of  the 
carbons,  the  resistance  of  the  arc  has  increased  to  an  extent 
which  can  be  predetermined,  the  increased  current  that  is 
thereby  passed  through  the  shunt  circuit  is  now  sufficiently 
strong  to  release  the  clutch  or  detent,  thus  permitting  the 
fall  or  feed  of  the  upper  carbon.  In  a  well  designed  lamp  this 
occurs  so  gradually  as  to  produce  no  perceptible  effect  on  the 
steadiness  of  the  light. 

Arc  lamps  are  generally  placed  in  series  circuits,  that 
is,  the  current  passes  successively  through  all  the  lamps 
in  the  circuit,  and  returns  to  the  source.  In  order  to  avoid 
the  breaking  of  the  entire  circuit,  an  automatic,  safety 
device  is  provided:  This  consists  essentially  of  an  electro- 
magnet placed  in  a  shunt  circuit,  so  that,  when  the  resist- 
ance of  the  arc  becomes  very  great,  the  increased  current, 
flowing  through  the  coils  of  the  electro-magnet,  produces  a 
movement  of  its  armature  which  closes  a  short  circuit  around 
the  lamp,  and  thus  cuts  it  out  of  the  circuit.  (See  Device, 
Safety.) 

Arc  lamps  assume  a  great  variety  of  forms.  A  well  known 
form  is  shown  in  Fig.  265. 

Lamp  Bracket,  Electric (See  Bracket,  Lamp.) 

Lamp,  Carcel (See  Carcel  Lamp.) 

Lamp,  Differential  Arc  —  — An  arc  lamp  in  which 
the  movements  of  the  carbons  are  controlled  by  the  differen- 


370  A  DICTIONARY  OF  ELECTRICAL 

tial  action  of  two  magnets  opposed  to  each  other,  one  of 
whose  coils  is  in  the  direct,  and  the  other  in  a  shunt  circuit 
around  the  carbons. 

Sometimes  the  differential  coils  are  placed  on  the  same 
magnet  core. 

Lamp-Hours. — The  number  of  lamp-hours  is  obtained 
by  multiplying  the  number  of  lamps  by  the  average  numbe1* 
of  hours  during  which  they  are  burning. 

A  method  of  estimating  the  current  supplied  to  a  consumer 
by  counting  the  number  of  hours  each  lamp  is  in  service. 

To  convert  lamp-hours  to  watt-hours  multiply  the  number 
of  lamp-hours  by  the  number  of  watts  per  lamp.  The  watt- 
hours,  divided  by  746,  will  then  give  the  electrical  horse-power 
hours.  (See  Watt-Hours.') 

Lamp,  Incandescent  Electric An  electric 

lamp  in  which  the  light  is  produced  by  the  electric  incan- 
descence of  a  strip  or  filament  of  some  refractory  substance, 
generally  carbon. 

The  carbon  strip  or  filament  is  usually  bent  into  the  form 
of  a  horseshoe  or  arc,  and  placed  inside  a  glass  vessel,  called 
the  lamp  chamber.  This  vessel  is  exhausted  by  means  of  a 
mercury  pump,  generally  to  a  fairly  high  vacuum. 

In  order  to  insure  the  complete  removal  from  the  lamp 
chamber  of  all  the  air  it  originally  contained,  both  it  and  the 
carbon  strip  that  is  placed  within  it  are  maintained  at  a  high 
temperature  during  the  process  of  exhaustion.  This  tempera- 
ture in  practice  is  obtained  by  sending  the  current  through 
the  carbon  strip  as  soon  as  the  air  is  nearly  all  removed. 
Towards  the  end  of  the  pumping  operation  the  current  is 
increased  so  as  to  raise  the  carbons  to  their  full  brilliancy. 

This  latter  operation  is  termed  the  occluded-gas  process, 
and  is  essential  to  the  successful  sealing  of  an  incandescent 
lamp.  By  its  means,  a  considerable  quantity  of  air  or  other 
gaseous  substances  shut  up  or  occluded  by  the  carbon,  is 


WORDS,  TERMS  AND  PHRASES.  371 

driven  out  of  the  carbon,  which  it  would  be  impossible  to  get 
rid  of  by  the  mere  operation  of  pumping.  In  order  to  insure 
the  success  of  the  operation  it  is  necessary  that  the  heating 
must  take  place  while  the  lamp  is  being  exhausted,  since 
otherwise  the  expelled  gases  would  be  reabsorbed.  (S<UJ 
Gases,  Occlusion  of.) 

The  exhaustion  continues  up  to  the  moment  the  lamp  cham- 
ber is  hermetically  sealed. 

The  lamp  chamber  is  usually  hermetically  sealed  by  the 
fusion  of  the  glass  in  the  manner  adopted  in 
the  sealing  of  Geissler  tubes,  or  Crooke's  radio- 
meters. 

For  the  preparation  of  the  carbon  strip,  its 
carbonization,  and  the  flashing  of  the  strip 
see  Carbonization,  Processes  of,  and  Flashing 
of  Carbons,  Process  for. 

The  ends  of  the  carbon  strip,   or  arc,   are 
attached  to  leading-in  ivires  of  platinum  that , 
pass  through  the  glass    walls  of   the    lamp 
chamber,  and  are  fused  therein  by  melting  the 
glass  around  them,  in  the  same  manner  as  are         fiff-  266. 
the  leading-in  wires  in  Geissler  tubes  and  other  similar  ap- 
paratus. 

Incandescent  lamps  are  generally  connected  to  the  leads  or 
circuits,  in  multiple-arc,  or  in  multiple-series  circuits;  they 
are,  however,  sometimes  connected  to  the  line  in  series.  (See 
Circuits,  Varieties  of.) 

In  the  former  case  their  resistance  is  comparatively  high  ; 
in  the  latter  case,  comparatively  low. 

Incandescent  electric  lamps  assume  a  variety  of  different 
forms.  One  of  them  is  shown  in  Fig.  266.  The  lamp 
chamber  conforms  in  general  shape  to  the  outline  of  the 
filament. 

Lamp,  Semi-Incandescent  Electric  — An 

electric  lamp,  in  which  the  light  is  due  to  the  combined  effects 


372 


A  DICTIONARY  OF  ELECTRICAL 


of  a  voltaic  arc,  and  electric  incandescence.  In  the  Keynier 
semi-incandescent  lamp,  shown  in  Fig.  267,  a  thin  pencil  of 
carbon  C,  is  g-ently  pressed  against  a  block  of  graphite  B.  A 
lateral  contact  is  provided  at  L,  through  a  block  of  graphite 
I,  by  means  of  which  the  current  is  conveyed  to  the  lower 
part  only  of  the  movable  rod  C,  which  part  alone  is  rendered 
incandescent. 

In  this  lamp  the  light  is  due  to  both  the  incandescence  of 
c  the  rod  C,  and  to  the  small  arc 

formed  at  J,  between  its  lower 
end  and  the  contact  block  B, 
though  mainly  from  the  latter. 

Latent    Electricity.— A 

term  formerly  applied  to  bound 
electricity.  Now  in  disuse.  (See 
Bound,  Dissimulated  or  Dis- 
guised Electricity.) 

Lateral  Discharge. — A 

small  discharge  observed  on  the 
discharge  of  a  Ley  den  jar,  be- 
tween parts  of  the  jar  not  in  the 
circuit  of  the  main  discharge. 

If    a  charged  Leyden    jar    is 
placed  on  an  insulating  stool,  and 
Fig.  261.  is  then  discharged  by  the  dis- 

charging rod,  the  lateral  discharge  is  seen  as  a  small  spark 
that  passes  between  the  outside  coating  of  the  jar  and  a  body 
connected  with  the  earth  at  the  moment  of  the  discharge 
through  the  rod.  This  lateral  discharge  is  due  to  a  small 
excess  of  free  electricity  on  the  outside,  that  is  not  neutralized 
by  the  opposite  charge. 

A  lateral  discharge  is  also  seen  in  the  sparks  that  can  be 
taken  from  a  conductor  in  good  connection  with  the  earth,  by 
holding  the  baud  near  the  conductor,  while  it  is  receiving 


WORDS,  TERMS  AND  PHRASES.  373 

large  sparks  from  a  powerful  machine  in  operation.  These 
discharges  are  due  to  induction. 

Lateral  Induction.— Induction  observed  between  closely 
approached  portions  of  a  circuit,  through  which  the  disruptive 
discharge  of  a  Leyden  jar  is  passed  as  a  long  spark,  thereby 
making  the  resistance  of  the  circuit  high. 

A  long  copper  wire,  bent  in  the  form  of  an  open  rectangle, 
has  its  free  ends  bent  near  their  extremities  so  as  to  approach 
eacli  other  until  but  half  an  inch  apart.  The  extreme  end  of 
one  of  the  extremities  is  provided  with  a  metallic  ball,  and 
the  other  end  connected  with  the  earth.  If,  now,  a  Leyden 
jar  charge  is  passed  through  the  wire,  by  connecting  the  outer 
coating  with  the  end  of  the  earth  connected  wire,  and  hold- 
ingthe  inside  coating  near  the  knob,  a  spark  will  pass  through 
the  half  inch  of  air  space  between  the  approached  portions 
of  the  circuit. 

This  discharge  is  due  to  what  was  called  formerly  lateral 
induction.  The  discharge  from  the  approached  parts  of  the 
wire  is  probably  to  be  regarded  as  a  branch  discharge,  or  shunt 
current,  due  to  the  fact  that  the  accumulated  resistance  of 
the  wire  to  the  current  of  the  disruptive  discharge,  becomes 
greater  than  that  of  the  air  space  between  the  approached 
parts  of  the  wire. 

Law,  Natural — A  correct  expression  of  the 

order  in  which  the  causes  and  effects  of  natural  phenomena 
follow  one  another. 

The  law  of  gravitation,  for  example,  correctly  expresses  the 
order  of  sequence  of  the  phenomena  which  result  when  unsup- 
ported bodies  fall  to  the  earth.  It  should  be  carefully  borne 
in  mind,  however,  that  natural  laws  cannot  be  regarded  as 
explaining  the  ultimate  causes  of  natural  phenomena,  but 
merely  express  their  order  of  occurrence  or  sequence. 

We  are,  ignorant,  for  example,  of  the  true  cause  of  gravita- 
tion and  are  only  acquainted  with  its  effects.  This  is  true  of 


8?4  A  DICTIONARY  OF  ELECTRICAL 

all  ultimate  physical  causes,  save  for  the  belief  in  their  origin 
in  a  Divine  will. 

Laws,  Ampere's or  Laws  of  Electro-Dyna- 
mic Attraction  and  Rcpul§ion. — Laws  expressing  the 
attractions  and  repulsions  of  electric  circuits  on  one  another. 

Laws,  Becquerel's or  Laws  of  magneto- 
Optic  Rotation. — Laws  of  the  magneto-optic  rotation  of 
the  plane  of  polarization  of  light.  (See  Magneto-  Optic  Rota- 
tion.) 

Laws  of  Coulomb,  or  Laws  of  Electrostatic  and 
Magnetic  Attractions  and  Repulsions.— Laws  for  the 

force  of  attraction  and  repulsion  between  charged  bodies  or 
between  magnet  poles. 

The  fact  that  the  force  of  electrostatic  attraction  or  repul- 
sion between  two  charges,  is  directly  proportional  to  the 
product  of  the  quantities  of  electricity  of  the  two  charges  and 
inversely  proportional  to  the  square  of  the  distance  between 
them,  is  known  as  Coulomb's  Law.  Coulomb  also  ascertained 
that  the  attractions  and  repulsions  between  magnet  poles  is 
directly  proportional  to  the  product  of  the  strength  of  the  two 
poles,  and  inversely  proportional  to  the  square  of  the  distance 
between  them.  This  is  also  called  Coulomb's  Law. 

Laws  of  Faraday,  or  Laws  of  Electrolysis.— Laws 

for  the  effects  of  electrolytic  decomposition.    (See  Electrolysis.) 

Laws  of  Kirchoff,  or  Laws  of  Shunt-Circuits.— 

The  laws  of  branched  or  shunted  circuits. 

These  laws  may  be  expressed  as  follows  : 

(1)  In  any  number  of  conductors  meeting  at  a  point,  if  cur- 
rents flowing  to  the  point  be  considered  as  -(-,  and  those  flow- 
ing away  from  it  as  — ,  the  algebraic  sum  of  the  meeting  cur- 
rents will  be  zero. 

This  is  the  same  thing  as  saying  as  much  electricity  must 
flow  away  from  the  point  as  flows  toward  it. 


WORDS,  TERMS  AND  PHRASES.  375 

(2)  In  any  system  of  closed  circuits  the  algebraic  sura  of  the 
products  of  the  currents  into  the  resistances  is  equal  to  the 
electro-motive  force  in  the  circuit. 

In  this  case  all  currents  flowing  in  a  certain  direction  are 
taken  as  positive,  and  those  flowing  in  the  opposite  direction 
as  negative.  All  electro-motive  forces  tending  to  produce 
currents  in  the  direction  of  the  positive  cm-rent  are  taken  as 
positive,  and  those  tending  to  produce  currents  in  the  oppo- 
site direction,  as  negative. 

E 

This  follows  from  Ohm's  law;  for,  since  C  =  — ,  the  electro- 

R 

motive  force  E  =  CR,  and  this  is  true  no  matter  now  often 
the  circuit  is  branched. 

Laws  of  Lenz. — Laws  for  determining  the  directions  of 
the  currents  produced  by  electro  magnetic  or  electro  dynamic 
induction.  (See  Lenz's  Law.} 

Law  of  Ohm,  or  Law  for  Current  Strength.— A 
fundamental  law  for  determining  the  current  strength  in  any 
circuit. 

The  strength  of  the  current  in  any  circuit  is  directly  pro- 
portional to  the  electro-motive  force,  and  inversely  propor- 
tional to  the  resistance  of  the  circuit. 
E 

C  =  — ,  or  E  =  C  R.     (See  Ohm's  Law.) 
R 

Law  of  Volta,  or  Law  for  Contact-Series. — A  law 
for  the  differences  of  electric  potential  produced  by  the  con- 
tact of  dissimilar  metals  or  other  substances. 

"  The  difference  of  potential  between  any  two  metals  is 
equal  to  the  sum  of  the  differences  of  potential  between  the 
intervening  substances  in  the  contact-series."  (See  Contact 
Electricity.  Contact-Series.) 

Layer,  Crookes' A  layer,  or  stratum,  in  the 

residual  atmosphere  of  a  vacuous  space,  in  which  the  mole- 
cules recoiling  from  a  heated  or  electrified  surface  do  not 


876  A  DICTIONARY  OF  ELECTRICAL 

meet  other  molecules,  but  impinge  on  the  walls  of  the  vessel 
directly  opposite  to  such  heated  surface. 

A  Crookes'  layer  may  result  as  the  effect  of  two  different 
causes,  viz.  : 

(1)  The  rarefaction  of  the  gas  is  such  that  the  distance  be- 
tween the  walls  of  the  vessel  and  the  heated  surface  is  less 
than  the  mean  free  path  of  the  molecules. 

(2)  The  wall  is  so  near  the  heated  surface  that  the  distance 
between  the  two  is  less  than  the  actual  mean  free  path  of  the 
molecules.     Under  these  last  named  circumstances,  Crookes' 
layers  may  result  whatever  be  the  density  of  the  gas. 

Lead  of  Brushes  of  Dynamo-Electric  Machine. 
(See  Angle  of  Lead.) 

Leading  Horns  of  Dynamo-Electric  Machine<> 
(See  Horns,  Leading,  of  Dynamo  Electric  Machine.) 

Leads. — The  main  conductors  of  any  system  of  electric  dis- 
tribution. 

The  leads,  or  main  conductors  in  a  multiple  system  of  incan- 
descent lighting,  must  maintain  a  constant  potential  at  the 
lamp  terminals.  The  dimensions  of  the  leads  are  therefore  so 
proportioned  as  to  absorb  as  small  an  amount  of  potential  as 
possible.  Since  in  incandescent  lighting,  where  the  lamp  is 
connected  to  the  leads  in  multiple-arc,  the  total  resistance  of 
the  lamps  is  comparatively  small,  the  resistance  of  the  leads 
must  necessarily  be  quite  small  in  order  to  avoid  a  marked 
drop  of  potential.  Comparatively  large  conductors  must 
therefore  be  used. 

The  main  conductor  for  series  circuits,  such  as  for  arc  lights, 
has  in  all  parts  the  same  current  strength.  Since  the  resist- 
ance of  the  lamp  in  such  a  circuit  is  quite  high,  a  compara- 
tively high  resistance  in  the  conductor  can  be  employed  with- 
out a  proportionally  large  absorption  of  potential.  Com- 
paratively small  conductors  can  therefore  be  used.  (See  Sys- 
tems of  Current  Distribution  by  Constant  and  by  Alternating 
Currents.) 


WORDS,  TERMS  AND  PHRASES.  377 

Leakage,  Electric The  gradual  dissipation  of  a 

charge  or  current  due  to  insufficient  insulation. 

Some  leakage  occurs  under  nearly  all  circumstances.  On 
telegraph  lines,  during  wet  weather  the  leakage  is  often  so 
great  as  to  interfere  with  the  proper  working  of  the  lines. 

The  leakage  of  a  well  insulated  conductor,  placed  in  a  high 
vacuum,  is  almost  inappreciable.  Crookes  has  maintained 
electric  charges  in  his  high  vacua  for  years  without  appre- 
ciable loss. 

Leakage  Conductor. — A  conductor  placed  on  a  tele- 
graph circuit,  to  prevent  the  disturbing  effects  of  leakage  into 
a  neighboring  line  by  providing  a  direct  path  for  such  leakage 
to  the  earth. 

The  leakage  conductor,  as  devised  by  Varley,  consists  of  a 
thick  wire  attached  to  the  pole.  The  lower  end  of  the  con- 
ductor is  well  grounded,  and  its  upper  end  projects  above  the 
top  of  the  pole. 

There  exists  some  doubt  in  the  minds  of  experienced  tele- 
graph engineers  whether  it  is  well  to  apply  leakage  conductors 
to  telegraphic  or  telephonic  lines  of  over  12  or  15  miles  in 
length,  since  such  conductors  greatly  increase  the  electro- 
static capacity  of  the  line,  and  thus  cause  serious  retardation. 

Leakage,  Magnetic  • A  useless  dissipation  of 

the  lines  of  magnetic  force  of  a  dynamo-electric  machine,  or 
other  similar  device,  by  their  failure  to  pass  through  the 
armature.  (See  Magnetophone.) 

Leclanche's  Voltaic  Cell.    (See  Cell,  Voltaic.) 
Legal  Ohm.— The  resistance  of  a  column  of  mercury 
one  square  millimetre  in  cross-section  and  106  centimetres  in 
length,  at  the  temperature  of  0°  C.  or  32°  F.    (See  B.  A.  Unit.) 
1  Ohm  =  1.00112  B.  A.  Unit.     This  value  of  the  ohm  was 
adopted  by  the  International  Electric  Congress,  in  1884,  as  a 
value  that  should  be  accepted  internationally  as  the  true 
value  of  the  ohm. 


378  A  DICTIONARY  OP  ELECTRICAL 

Length  of  Spark.— The  length  of  spark' that  passes 
between  two  charged  conductors  depends  : 

(1)  On  the  difference  of  potential  between  them. 

(2)  On  the  character  of  the  gaseous  medium  that  separates 
the  two  conductors. 

(3)  On  the  density  or  pressure  of  the  gaseous  medium  be- 
tween the  conductors.     Up  to  a  certain  pressure,  a  decrease 
in  the  density  causes  an  increase  in  the  length  of  the  distance 
the  spark  will  pass.     When  this  limit  is  reached,  a  further 
decrease  of  density  decreases  the  length  of  spark.     A  high 
vacuum  prevents  the  passage  of  a  spark  even  under  great 
differences  of  potential. 

(4)  On  the  kind  of  material  that  forms   the  electrodes  be- 
tween which  the  charges  pass. 

(5)  On  the  shape  of  the  charged  conductor. 

(6)  On  the  direction  of  the  current.     Sparks  from  the  prime 
conductor  are  denser  and  more  powerful  than  those  from  the 
negative  conductor. 

It  will  be  observed  that  the  length  of  the  spark  practically 
depends  mainly  on  two  circumstances,  viz.,  on  the  differences 
of  potential  of  the  opposite  charges,  and  the  conducting 
power  of  the  medium  that  separates  the  two  bodies. 

Lenz'  Law. —  The  direction  of  the  currents  set  up  by 
electro-magnetic  induction  is  always  such  as  to  tend  to  op- 
pose the  motion  producing  them. 

Letter-Boxes,  Electric Various  devices  that 

announce  the  deposit  of  a  letter  in  a  box,  by  the  ringing  of  a 
bell  or  the  movement  of  a  needle  or  index. 

These  devices  generally  act  by  the  making  or  opening  of  an 
electric  circuit  by  the  fall  of  the  letter  in  the  box. 

Ley  den  Jar.    (See  Jar,  Ley  den.) 

Leyden-Jar  Battery.    (See  Battery,  Leyden  Jar.) 

Lichtenberg's  Figures.    (See  Figures,  Lichteriberg.) 


WORDS,  TERMS  AND  PHRASES.  379 

Life  of  Electric  Incandescent  Lamps.— The  num- 
ber of  hours  that  an  incandescent  electric  1  amp,  when  traversed 
by  the  normal  current,  will  continue  to  afford  a  good  com- 
mercial light. 

The  failure  of  an  electric  incandescent  lamp  results  either 
from  the  volatilization  or  rupture  of  the  carbon  conductor,  or 
from  the  failure  of  the  vacuum  of  the  lamp  chamber.  Since 
the  employment  of  the  flashing  process,  and  the  process  for 
removing  the  occluded  gases  it  is  not  unusual  for  incandes- 
cent lamps  to  have  a  life  of  several  thousand  hours.  (See 
Flashing  Carbons,  Process  for.) 

Light,  Electro-Magnetic  Hypothesis  of A 

hypothesis  for  the  cause  of  light  proposed  by  Maxwell,  based 
on  the  relations  existing  between  the  phenomena  of  light 
and  those  of  electro-magnetism. 

Maxwell's  electro-magnetic  theory  of  light  assumes  that 
the  phenomena  of  light  and  magnetism  are  each  due  to  cer- 
tain motions  of  the  ether.  Electricity  and  magnetism  being 
due  to  its  rotations  or  oscillations,  and  light  to  its  to--and-fro 
motions. 

He  proposed  this  theory  to  show  that  the  phenomena  of 
light,  heat,  electricity  and  magnetism  could  all  be  explained 
by  one  and  the  same  cause,  viz. ,  a  vibratory  or  oscillatory 
motion  of  the  particles  of  the  hypothetical  ether.  Maxwell 
died  before  completing  his  hypothesis,  and  it  has  never  since 
been  sufficiently  developed  to  thoroughly  entitle  it  to  the 
name  of  a  theory. 

There  are,  however,  numerous  considerations  which  render  it 
probable  that  electric  and  magnetic  phenomena,  like  those  of 
light  and  heat,  have  their  origin  in  a  vibratory  or  oscillatory 
motion  of  the  luminiferous  ether.  A  few  of  these,  as  pointed 
out  by  Maxwell,  S.  P.  Thompson,  Lodge,  Larden  and  others, 
are  as  follows : 

(1)  It  is  quite  possible  that  the  thing  called  electricity  is  the 
ether  itself ;  negative  electrification  consisting  in  an  excess  of 


380  A  DICTIONARY  OF  ELECTRICAL 

the  ether,  and  positive  electrification  in  a  deficit.  (See  Hy- 
potheses of  Electricity.) 

(2)  It  is  possible  that  electrostatic  phenomena  consist  in  a 
strain  or  deformation  of  the  ether.     A  dielectric  may  differ 
from  a  conductor  in  that  the  former  may  have  such  an  attrac- 
tion for  the  ether  as  to  give  it  the  properties  of  an  elastic 
solid,  while  in  the  latter  the  ether  is  so  free  to  move  that  no 
strain  can  possibly  be  retained  by  it.      (See  Dielectric.   Con- 
ductor.) 

(3)  Dielectrics  are  transparent  and  conductors  are  opaque. 
There  are  exceptions  to  this  in  the  case  of  vulcanite  and 

many  other  excellent  dielectrics.  Nor  should  this  similarity 
be  expected  to  be  general  in  view  of  the  difference  between 
diathermancy  and  transparency. 

(4)  It  is  possible  that  an  electric  current  consists  of  a  real 
motion  of  translation  of  the  ether  through  a  conductor. 

(5)  It  is  possible  that  electro-motive  force  results  as  differ- 
ences of  ether  pressures,  this  would  of  course  follow  from  (4). 

(6)  The  vibrations  of  light  are  propagated  in  a  direction  at 
right  angles  to  the    direction  in  which  the  light  is  moving. 
The  magnetic  field  of  a  current  is  propagated  in  planes  at 
right  angles  to  the  direction  in  which  the  current  is  flowing. 

(7)  It  is  possible  that  lines  of  electrostatic  and  magnetic 
force  consist  of  chains  of  polarized  ether  particles. 

(8)  The  velocity  of  propagation  of  light  agrees  very  nearly 
with  the  velocity  of  propagation  of  electro-magnetic  induc- 
tion.    (See  Velocity  Ratio.) 

(9)  In  certain  axial  crystals  the  difference  of  transparency 
in  the  direction  of  certain  axes,  corresponds  with  the  direc- 
tion in  which  such  crystals  conduct  electricity. 

L.ight-Hou§e   Illumination,    Electric   

The  application  of  the  electric  arc  light  to  the 

illumination  of  light  houses. 

A  powerful  arc  light  is  placed  in  the  focus  of  the  dioptric 
lens  now  commonly  employed  in  light  houses.     Since  the  con- 


WORDS,  TERMS  AND  PHRASES. 


381 


sumption  of  the  carbon  electrodes  would  alter  the  position 
of  the  focus  of  the  light,  electric  lamps  for  such  purposee  ^re 
constructed  to  feed  both  of  their  carbons  instead  of  the  upper 
carbon  only,  as  in  the  case  of  the  ordinary  arc  lamp. 

Light,    Intensity    of- (See    Intensity    of  Light. 

Photometer.) 

Lighting,  Central  Station The  lighting  of  a 

number  of  houses  or  other  buildings  from  a  single  station, 
centrally  located. 

Central  station  lighting  is  distinguished  from  isolated 
lighting,  by  the  fact  that  a  number  of  separate  buildings, 
houses,  or  areas  are  lighted  by  the  current  produced  at  a 
single  station,  centrally  located,  instead  of  fron?  a  number  of 
separate  electric  sources  located  in  each  of  the  houses,  etc., 
to  be  lighted.  (See  Systems  of  Electric  Distribution.) 

Lightning.— The  spark  or  bolt  that  results  from  the  dis- 
charge of  a  cloud  to  the  earth,  or  to  a  neighboring  cloud. 
(See  Atmospheric  Electricity.  Kite,  Franklin's.) 

Lightning  Arrester.— A  device,  by  means  of  which  the 
apparatus  placed  in  any  electric  circuit  are  protected  from 
the  destructive  effects  of  a  flash  or  bolt  of  lightning. 

In  the  phenomena  of  lateral  induction  we  have  seen  ths 
tendency  of  a  disruptive  discharge  to  take  a  short  cut  across 
an  intervening  air  space,  rather  than  through  a  longer  though 
better  conducting  path.  Most  lightning  arresters  are  depend- 
ent for  their  operation  on  this  tendency  to  lateral  discharge. 
(See  Induction,  Lateral.  Discharge,  Disruptive.) 

A  form  of  lightning  arrester  is  shown  in  Fig.  268. 

The  line  wires  A  and  B,  are  connected  by  two  metallic  plates 
to  C  and  D,  respectively. 

These  plates  are  provided  with  points,  as  shown,  and  placed 
near  a  third  plate,  connected  to  the  ground  by  the  wire  G. 
Should  a  bolt  strike  the  line,  it  is  discharged  to  the  earth, 
through  the  wire  Gr. 


382  A  DICTIONARY  OF  ELECTRICAL 

Lightning,  Back  or  Return  Stroke. — (See  Back  or 
Return  Stroke  of  Lightning.) 

Lightning,  Globular A  rare  form  of  light- 
ning, in  which  a  globe  of  fire  appears  for  a  while,  quietly 
floats  in  the  air,  and  then  explodes  with  great  violence. 

The  exact  cause  of  globular  lightning  is  unknown.  Phe- 
nomena allied  to  it,  however,  have  been  observed  by  Plant6 
during  the  discharge  of  his  rheostatic  machine,  when  dis- 
charged in  series,  or  for  a  great  difference  of  electric  potential. 
Similar  phenomena,  are  sometimes,  though  rarely,  observed 
during  the  discharge  of  a  powerful  Leyden  battery.  Sir  Wm. 
Thomson  ascribes  the  effect  to  an  optical  illusion. 


£J 

Fig.  268. 
Lightning,  Heat  or  Sheet,  Volcanic  and  Zigzag 

Heat  or  sheet  lightning  is  the  name  given  to  a  dis- 
charge unaccompanied  by  any  thunder  audible  to  the  observer, 
in  which  the  entire  surfaces  of  the  clouds  are  illumined. 

Its  cause  has  been  ascribed  to  the  reflection  from  the  clouds 
of  lightning  flashes  too  far  below  the  horizon  to  permit  them 
to  be  directly  seen,  or  the  thunder  to  be  audible, 


WORDS,  TERMS  AND  PHRASES.  383 

If  a  Geissler  tube,  which  contains  several  concentric  tubes, 
be  charged  by  a  Holtz  machine,  and  then  touched  at  different 
parts  by  the  hands,  a  succession  of  luminous  discharges  will 
be  seen  in  the  dark,  that  bear  a  remarkable  resemblance  to 
the  flashes  of  heat  or  sheet  lightning. 

Lightning  Rods.— A  rod,  or  wire  cable  of  good  conduct- 
ing material,  placed  on  the  outside  of  a  house  or  other  struc- 
ture,^ order  to  protect  it  from  the  effects  of  a  lightning  dis- 
charge. 

Lightning  rods  were  invented  by  Franklin.  The  result  of  a 
very  extended  inquiry  recently  made  on  the  subject,  leaves  no 
room  for  doubt  that  a  lightning  rod,  properly  constructed  and 
placed,  affords  an  efficient  protection  to  the  buildings  on 
which  it  is  placed. 

To  insure  this  protection,  however,  all  the  following  con- 
ditions must  be  carefully  fulfilled,  else  the  rod  may  prove  a 
source  of  danger  rather  than  a  protection,  viz. : 

(1)  The    rod,  generally   of    iron  or    copper,    should    have 
such  an  area  of  cross  section  as  to  enable  it  to  carry  without 
fusion  the  heaviest  bolt  it  is  liable  to  receive  in  the  latitude 
in  which  it  is  located.     When  of    iron,   the  area  of  cross 
section  should  be  about  seven  times  greater  than  when  of 
copper. 

(2)  The  rod  should  be  continuous  throughout,  all  joints  being 
carefully  avoided.     If  these  be  used  they  should  be  made  of  as 
low  resistance  as   possible  and  should   be    protected  against 
corrosion. 

(3)  The  upper  extremity  of  the  rod  should  terminate  in  one 
or  more  points  formed  of  some  metal  that  is  not  readily  cor- 
roded, such  as  platinum  or  nickel. 

(4)  The  lower  end  of  the  rod  should  be  carried  down  into 
the  earth  until  it  meets  permanently  damp  or  moist  ground, 
where  it  should  be  attached  to  a  fairly  extended  metallic  sur- 
face buried  in  the  ground.     Metallic  plates  will  answer  for  the 
purpose,  but,  if  gas  or  water  pipes  are  available,  the  rpd  should. 


384  A  DICTIONARY  OF  ELECTRICAL 

be  placed  in  good  electrical  connection  therewith,  by  wrapping 
-it  around  and  soldering  it  to  such  pipes. 

This  fourth  requirement  is  of  great  importance  to  the  pro- 
per action  of  a  lightning  rod,  and  unless  thoroughly  fulfilled 
may  render  the  rod  worthless,  no  matter  how  carefully  the  other 
requirements  are  attended  to.  When  a  bolt  strikes  a  light- 
ning rod  which  is  not  properly  grounded,  the  discharge  is  almost 
certain  to  destroy  the  building  to  which  the  rod  is  connected. 

(5)  The  rod  should  not  be  insulated  from  the  building,  un- 
less to  prevent  stains  from  the  oxidation  of  the  metal.    On  the 
contrary  it  should  be  directly  connected  with  all  masses  of  metal 
in  its  path,  such  as  tin  roofs,  gutter-spouts,  metallic  cornices, 
etc.     In  this  way  only  can  dangerous  disruptive  lateral  dis- 
charges from  the  rod  to  such  masses  of  metal  be  avoided. 

(6)  The  rod  should  project  above  the  roof  or  highest  part  of 
the  building,  or,  in  other  words,  the  height  of  the  rod  should 
bear  a  certain  proportion  to  the  size  of  the  building  to  be  pro- 
tected.    A  rod  will  protect  a  conical  space  around  it,  the 
radius  of  whose  base  is  equal  to  the  vertical  height  of  the  rod 
above  the  ground,  but  whose  sides  are  curved  inwards  instead 
of  being  straight.     Where  the  building  is  very  high,  a  num- 
ber of  separate  rods  all  connected  to  one  another  should  be 
employed. 

(7)  A  stranded  conductor  is  much  better  than  an  equal  cross 
section  of  a  solid  rod  of  the  same  metal. 

A  lightning  rod  more  frequently  acts  to  quietly  discharge 
an  impending  cloud  by  convective  discharge,  than  by  an  ac- 
tual disruptive  discharge  of  the  same.  (See  Discharge,  Con- 
vective. Discharge,  Disruptive.) 

Lightning  rods  should  be  frequently  tested  to  see  that  no 
breaks  or  oxidation  of  their  joints  have  occurred. 

Lightning  Rods  for  Ships.— A  system  of  rods  designed 
to  afford  electric  protection  for  vessels  at  sea. 

Since  the  lightning  discharge  takes  place  between  the 
points  of  greatest  difference  of  potential,  and  these  are  gener- 


WORDS,  TERMS  AND  PHRASES.  385 

ally  between  the  cloud  and  the  nearest  point  of  the  earth,  tall 
objects  are  especially  liable  to  be  struck. 

Ships  at  sea  should,  therefore,  be  thoroughly  protected  from 
lightning. 

In  Harris'  system  of  lightning  protection  for  ships,  the  rods 
are  connected  with  a  series  of  copper  plates  and  rods  so  placed 
on  the  masts  as  to  readily  yield  to  strains.  These  are  elec- 
trically connected  with  the  copper  sheathing  of  the  vessel  and 
with  all  large  masses  of  metal  in  the  vessel.  This  latter  precau- 
tion is  especially  necessary  in  the  case  of  men-of-war,  in  order 
to  protect  the  powder  magazine.  Harris'  method  for  the  light- 
ning  protection  of  ships,  which  was  adopted  only  after  very 
considerable  opposition,  proved  so  efficacious  in  practice  that 
serious  effects  of  lightning  on  vessels  so  protected  are  now 
almost  unknown.  In  1845,  Harris  received  the  honor  of 
knighthood  from  the  English  Government  for  his  services  in 
this  respect. 

A  lightning  rod  sometimes  fails  to  protect  a  house  or  barn 
from  the  fact  that  a  heated,  ascending  current  of  air  from  a 
fire  in  the  house,  or  from  the  gradual  heating  of  green  hay  or 
grain  in  the  barn,  increases  the  virtual  height  of  the  house 
beyond  the  ability  of  its  rod  to  protect  it. 

Lightning,  Volcanic The  lightning  dis- 
charges that  attend  most  volcanic  eruptions. 

Volcanic  lightning  is  probably  due  to  the  friction  of  volcanic 
dust  particles  against  one  another,  or  against  the  air,  but  par- 
ticularly to  the  sudden  condensation  of  the  vapor  that  is  gen- 
erally disengaged  during  volcanic  eruptions. 

Lightning,  Zigzag,  Chain  or  Forked  — 

The  commonest  variety  of  lightning  flashes  in  which  the  dis- 
charge apparently  assumes  a  forked  zigzag,  or  even  a  chain- 
shaped  path. 

This  form  is  seen  in  the  discharge  of  a  Holtz  machine,  or  of 
a  Ruhmkorff  Induction  Coil, 


386  A  DICTIONARY  OF  ELECTRICAL 

The  irregular  shape  of  the  path  is  probably  due  to  the 
resistance  of  solid  particles  in  the  air,  which  are  piled  up  in 
front  of  the  discharge,  or  to  the  effects  of  the  lateral  induc- 
tion that  is  produced  during  the  discharge.  (See  Induction, 
Lateral.) 

Line,  Neutral of  a  Magnet.— A  line  joining  the 

neutral  points  of  a  magnet,  or  the  points  approximately  mid- 
way between  the  poles. 

This  is  sometimes  called  the  equator  of  the  magnet. 

The  neutral  point  is  the  point  where  the  lines  of  force  out- 
side the  magnet  are  parallel  to  the  surface  of  the  magnet. 
(Hering.) 

Line,  Neutral of  Commutator  Cylinder.— A 

line  on  the  commutator  cylinder  of  a  dynamo-electric  machine, 
connecting  the  neutral  points,  or  the  points  of  maximum  posi- 
tive and  negative  difference  of  potential.  (See  Dynamo- 
Electric  Machine.) 

Line,  Telegraphic,  Telephonic,  etc. The 

conducting  circuit  provided  for  the  transmission  of  the  elec- 
tric impulses  or  currents  employed  in  any  system  of  electric 
transmission. 

Lines,  Aclinic,  or  Isoclinic Lines  connecting 

places  that  have  the  same  magnetic  inclination.  (See  Aclinic 
Line.  Isoclinic  Line.) 

Lines,  Agonic,  or  I§ogonic Lines  connecting 

places  that  have  an  equal  magnetic  declination.  (See  Agone.) 

Lines,  Isodynamic —      — (See  Isodynamic  Lines.) 

Lines  of  Electrostatic  Force.— Lines  extending  in  the 
direction  in  which  the  force  of  electrostatic  attraction  or  re- 
pulsion acts. 

Lines  of  electrostatic  force  pass  through  dielectrics;  whether 
the  force  acts  by  means  of  a  polarization  of  the  dielectric,  or 
by  means  of  a  tension  set  up  in  it,  is  not  known.  (See  Field, 
Electrotastic.) 


WORDS,  TERMS  AND  PHRASES.  387 

Lines  of  Force,  Direction  of Lines 

extending  in  the  direction  in  which  the  lines  of  magnetic  force 
are  assumed  to  pass. 

The  lines  of  magnetic  force  are  assumed  to  come  out  of  the 
north  pole  of  a  magnet,  and  to  pass  in  at  its  south  pole. 

The  lines  of  electrostatic  force  are  assumed  to  pass  out  of  a 
positively  charged  surface,  and  into  a  negatively  charged  sur- 
face. 

Lines  of  Magnetic  Force.— Lines  extending  in  the 
direction  in  which  the  force  of  magnetic  attraction  or  repul- 
sion acts.  (See  Field,  Magnetic.) 

Liquids,  Specific  Resistance  of The  resist- 
ance of  a  given  length  (one  centimetre)  and  cross  section  (one 
square  centimetre)  of  any  liquid  as  compared  with  the  resist- 
ance of  an  equal  length  and  cross  section  of  pure  silver. 
The  resistance  of  a  few  common  liquids  and  solutions  is  here 
given  from  Lupton  : 
Water,  pure  at  75°  C... 1.188  X  108  ohms 

i.  e.,  118,800,000. 

Water  at  4°  C 9.100  X  106       " 

Water  at  11°C 3.400  X  105       " 

Dilute  hydrogen  sulphate  (sulphuric  acid)  at 

18°  C.  5  per  cent,  acid 4.88 

Dilute   hydrogen  sulphate  at  18°  C.   3   per 

cent.acid 1.38  " 

Nitric  acid,  at  18°  C.  density  1.32... 1.61  " 

Saturated  solution  of  copper  sulphate  (blue 

vitriol)  at  10°  C ...29.30  " 

Saturated  solution  of  zinc  sulphate  at  143  C.  21.50  " 

Hydrochloric  acid,  20  per  cent,  acid,  at  18°  C.  1.34  " 

Sal  ammoniac,  25  per  cent,  salt 2.53  " 

Commonsalt,  saturated,  at  13°  C 5.30  " 

It  will  be  observed  that  the  resistance  varies  considerably 
with  differences  of  temperature. 


388  A  DICTIONARY  OF  ELECTRICAL 

Local  Action.— In  a  battery,  the  loss  of  energy  by  the 
irregular  and  wasteful  solution  of  the  zinc  or  positive  element 
by  the  electrolyte. 

The  local  action  of  a  battery  is  caused  by  the  solution  of  the 
zinc  or  positive  plate  by  the  action  of  local  voltaic  couples 
formed  by  couples  of  zinc  and  minute  particles  of  carbon,  lead, 
or  other  impurities.  It  is  remedied  by  the  amalgamation  of 
the  zinc.  (See  Zinc,  Amalgamation  of.) 

In  a  dynamo  electric  machine,  the  loss  of  energy  by  the 
setting  up  of  eddy  currents  in  the  conducting  masses  of  the 
pole-pieces,  cores,  etc.  (See  Currents,  Eddy.) 

In  a  dynamo'  electric  machine  local  action  is  obviated  by  a 
lamination  of  the  pole  pieces,  armature  core,  etc,  (See 
Lamination  of  Cores. ) 

Local  Battery.— (See  Battery,  Local.) 
Local  Currents.— (See  Currents,  Eddy.) 

Localization  of  Faults.— Determining  the  position  of 
a  fault  in  a  telegraph  line  or  cable  by  calculations  based  on  the 
fall  in  the  potential  of  the  line  measured  at  different  points 
or  by  loss  of  charge,  etc. 

For  description  see  standard  works. 

Locomotive,  Electric A  railway  engine  whose 

motive  power  is  electricity.     (See  Railroad  Electric.) 

Locomotive     Head-Light,     Electric (See 

Head-Light,  Electric.) 

Lodes  tone. — A  name  applied  by  the  ancients  to  an  ore 
of  iron  (magnetic  iron  ore),  that  naturally  possesses  the  power 
of  attracting  light  pieces  of  iron  to  it. 

Lodestone,  or  magnetic  iron  ore,  must  be  regarded  as  a 
magetizable  substance  that  has  become  permanently  magnetic 
from  its  situation  in  the  earth's  magnetic  field.  Such  beds  of 
ore  concentrate  the  lines  of  the  earth's  magnetic  field  on  them, 
and  thus  become  magnetic. 


WORDS,  TERMS  AND  PHRASES.  889 

Log;,  Electric An  electric  device  for  measuring1 

the  speed  of  a  vessel. 

Any  log  that  operates  by  the  rotation  of  a  wheel  is  caused 
to  register  the  number  of  rotations  by  a  step-by-step  recording 
apparatus  operated  by  breaks  in  the  circuit,  made  during-  the 
rotation  of  the  wheels,  at  any  given  number  of  turnsi  say  100, 
or  any  other  convenient  multiple.  Such  a  log  may  be  kept 
constantly  in  the  water,  and  observed  when  required,  or  it  can 
be  made  to  register  a  permanent  record  of  its  actual  speed  at 
any  time  during  the  entire  run. 

Logarithms. — The  logarithm  of  any  given  number,  is  the 
exponent  of  the  power  to  which  it  is  necessary  to  raise  a  fixed 
number,  in  order  to  produce  the  given  number. 

A  table  of  logarithms  enables  the  operations  of  multiplica- 
tion, division,  and  the  extraction  of  roqts,  to  be  readily  per- 
formed by  simple  multiplication,  division,  addition  or  subtrac- 
tion. When  thoroughly  understood,  logarithms  greatly  re- 
duce the  labor  of  mathematical  calculations.  For  the  manner 
in  which  they  are  used  the  student  is  referred  to  any  standand 
work  on  mathematics. 


Longitude,  Electrical  Determination  of 


The  determination  of  the  longitude  of  a  place,  by  differ- 
ences in  time  between  it  and  a  place  on  the  prime  meridian,  as 
simultaneously  determined  telegraphically. 

In  determinations  of  this  character  allowance  must  be  made 
for  the  retarding  effects  of  long  telegraphic  lines,  or  cables. 

Loop,  Electric A  portion  of  a  main  circuit 

consisting  of  a  wire  going  out  from  one  side  of  a  break  in  the 
main  circuit  and  returning  to  the  other  side  in  the  break. 

Loops  are  employed  for  the  purpose  of  connecting  a  branch 
telegraph  office  with  the  main  line  ;  for  placing  one  or  more 
electric  arc  lamps  on  the  main  line  circuit ;  for  connecting  a 
messenger  call,  or  telephone  circuit  with  a  main  line ;  and  for 
numerous  similar  purposes. 


396 


A  DICTIONARY  OP  ELECTRICAL 


I  ,o  \o< I  rog; r:i  |»  11 . — An  apparatus  for  electrically  recording 
on  paper  the  actual  course  of  a  ship  by  the  combined  action  of 
magnetism  and  photography. 

Luces. — Plural  of  lux.    (See  Lux.) 

l.u \. — A  name  proposed  by  Preece  for  the  unit  of  inten- 
sity of  illumination. 

One  lux  is  the  illumination  given  by  a  standard  candle  at  the 
distance  of  12.7  inches. 

One  lux  is  .the  illumination  given  by  a  carcel  at  the  distance 
of  one  metre. 

One  lux  is  the  illumination  given  by  a  lamp  of  1,000  candles 
at  105.8  feet.  (See  Illumination,  Unit  of  .) 


Machine,  Frictional  Electric 


Mg.  271. 


A  machine  for  the  de- 
velopment of  electric- 
ity by  friction. 

A  frictional  electric 
machine  consists  of  a 
plate  or  cylinder  of 
glass  A,  Fig.  271,  ca- 
pable of  rotation  on  a 
horizontal  axis. 

A  rubber  formed  of  a 
chamois  skin,  covered 
with  an  amalgam  of  tin 
and  mercury,  is  placed 
at  B.  By  the  rotation 


of  the  plate  the  rubber  becomes  negatively,  and  the  glass 
positively  excited.  An  insulated  conductor  D,  called  the 
prime  or  positive  conductor,  provided  with  a  comb  of  points, 
becomes  positively  charged  by  induction.  The  machine 
will  develop  electricity  best  if  a  conductor  attached  to  the 


WORDS,  TERMS  AND  PHRASES. 


391 


rubber   is   connected  with  the  ground,   as  by  a  chain,    as 
shown. 


Machines,    Electrostatic    Induction 


or  Influence  Machines.— Machines  in  which  a  small 
initial  charge  produces  a  greatly  increased  charge  by  its  in- 
ductive action  on  a  rapidly  rotated  disc  of  glass. 

An  excellent  type  and  example  of  such  a  machine  is  found 
in  the  Holtz  machine  which  consists  of  the  following  parts, 
as  shown  in  Fig.  272,  viz.  : 

(1)  A  stationary  glass  plate  A,  fixed  at  its  edges  to  insulated 
supports. 

(2)  A  movable  plate  B,  capable  of  rapid  rotation  on  a  hor- 
izontal axis,  by  a  driv- 
ing pulley. 

(3)  Armatures  of  var- 
nished   paper  /,  /, 
placed  on  opposite  sides 
of   the  fixed    plate    at 
holes  or  windows  P,  P', 
cut  in  the  plate.     The 
armatures    are    placed 
on  the  side  of  the  fixed 
plate    away   from   the 
moving  plate,  or  on  the 
back  of  the   plate,  so 
that  the  plate,   on  its 


Fig.  272. 


rotation,  moves  towards  tongiies  of  paper  attached  to  the 
middle  of  the  armature. 

(4)  Metal  combs  placed  in  front  of  the  movable  disc  oppo- 
site the  armatures,  .and  connected  with  the  brass  balls  m,  n, 
one  of  which  is  movable  towards  and  from  the  other  by 
means  of  a  suitably  supported  insulating  handle  connected 
with  it. 


&93  A  DICTIONARY  OP  ELECTRICAL 

A  small  initial  charge  is  given  to  one  of  the  armatures  by 
holding  a  plate  of  electrified  vulcanite  on  it,  and  rotating  the 
machine  while  the  balls  m,  n,  are  in  contact.  As  soon  as  the 
machine  is  charged  the  balls  are  gradually  separated,  when  a 
torrent  of  sparks  will  pass  between  them  so  long  as  the  plate 
is  rotated. 

When  the  balls  are  separated  too  far  the  sparks  cease  to 
pass.  The  balls  must  then  be  again  brought  into  contact  and 
gradually  separated  as  before. 

The  Holtz  machine  can  be  regarded  as  a  revolving  electro- 
phorus  provided  with  means  for  constantly  discharging  and 
recharging  the  upper  metallic  plate.  (See  Electrophorus). 

The  action  of  the  machine  is  well  described  by  S.  P.  Thomp- 
son in  his  "  Elementary  Lessons  on  Electricity  and  Magnetism," 
as  follows : 

"  Suppose  a  small  -f-  charge  to  be  imparted  at  the  outset  to 
the  right  armature  / ;  this  charge  acts  inductively  across  the 
discs  upon  the  metallic  comb,  repels  electricity  through  it, 
and  leaves  the  points  negatively  electrified.  They  discharge 
negatively  electrified  air  upon  the  front  surface  of  the  mov- 
able disc  ;  the  repelled  charge  passes  through  the  brass  rods 
and  balls,  and  is  discharged  through  the  left  comb  upon  the 
front  side  of  the  movable  disc.  Here  it  acts  inductively  upon 
the  paper  armature,  causing  that  part  of  it  which  is  opposite 
itself  to  be  negatively  charged  and  repelling  a  -)-  charge  into  its 
farthest  part,  viz.,  into  the  tongue,  which  being  bluntly 
pointed,  slowly  discharges  a  -j-  charge  upon  the  back  of  the 
movable  disc.  If  now  the  disc  be  turned  round,  this  -(-  charge 
on  the  back  comes  over  from  the  left  to  the  right  side,  in  the 
direction  indicated  by  the  arrow,  and,  when  it  gets  opposite 
the  comb,  increases  the  inductive  effect  of  the  already  existing 
-(-  charge  on  the  armature,  and  therefore  repels  more  electricity 
through  the  brass  rods  and  knobs  into  the  left  comb.  Mean- 
time the  —  charge,  which  we  saw  had  been  induced  in  the  left 


WORDS,  TERMS  AND  PHRASES. 


armature,  has  in  turn  acted  on  the  left  comb,  causing  a  -|- 
charge  to  be  discharged  by  the  points  upon  the  front  of  the  disc ; 
and,  drawing  electricity  through  the  brass  rods  and  knobs,  has 
made  the  right  comb  still  more  highly  — ,  increasing  the  dis- 
charge of  —  ly  electrified  air  upon  the  front  of  the  disc,  neu- 
tralizing the  -f-  charge 
which  is  being  con- 
veyed over  from  the 
left.  These  actions  re- 
sult in  causing  the  top 
half  of  the  moving  disc 
to  be  —  ly  electrified. 
The  charges  on  the 
front  serve  as  they  are 
carried  round,  to  neu- 
tralize the  electricities 
let  off  by  the  points  of 
the  combs,  while  the 
charges  on  the  back,  m-  Fjff-  S7S- 

duced  respectively  in  the  neighborhood  of  each  of  the  arma- 
tures, serve,  when  the  rotation  of  the  disc  conveys  them 
round,  to  increase  the  inductive  influence  of  the  charge  on 
the  other  armature." 

The  student  will  be  aided  in  following  Prof.  T.'s  explanation 
by  the  diagrammatic  sketch,  shown  in  Fig.  273.  Here  the  rotat- 
ing plate  is  shown  for  convenience  in  the  form  of  a  cylinder. 
Tin-  armatures  are  shown  on  the  back  of  the  plate  at  /  and/, 
opposite  the  brass  collecting  combs  P'  and  P,  with  their  dis- 
charging rods  and  balls  a  a. 

The  effect  of  the  positive  charge  given  to  the  right  hand 
armature/',  directly  through  the  combs  P',  rods  a  a,  comb  P, 
1o  loft,  hand  armature  /,  is  readily  seen.  The  rotation  of 
the  plate  being  In  the  direction  of  the  curved  arrows,  the 
charging  of  the  front  of  the  plate  by  convection  streams 
from  the  combs,  and  the  back  of  the  plate  from  the  points 


394  A  DICTIONARY  OF  ELECTRICAL 

of  the  paper  armatures,  as  well  as  the  character  of  the 
charge  will  be  understood.  There  thus  results,  as  is  shown, 
a  positive  charge  on  both  the  front  and  back  of  the  upper 
half  of  the  rotating  plate,  and  a  negative  charge  on  both 
sides  of  its  lower  half.  A  reversal  of  polarity  of  the  plate 
occurs  at  the  line  P  a  a  P'.  Sometimes  the  reversal  does  not 
occur  and  the  machine  either  loses  its  charge  entirely,  or 
in  part.  A  conductor  S  S,  furnished  with  points,  is  sometimes 
provided  to  lessen  the  chances  of  lack  of  reversal. 

machines,  Faradic •  —(See  Faradie  Machines.) 

Hade  Circuit.— (See  Circuit,  Closed.) 

IVIagnc-Crystallic  Action. — A  term  proposed  by  Fara- 
day to  express  the  differences  in  the  action  of  magnetism  on 
crystalline  bodies  in  different  directions. 

A  needle  of  tourmaline  if  hung  with  its  axis  horizontal  is  no 
longer  paramagnetic  as  usual,  but  diamagnetic.  The  same  is 
true  of  a  crystal  of  bismuth.  Faraday  concluded  from  these 
experiments  that  a  force  existed  distinct  from  the  paramag- 
netic or  diamagnetic  force.  He  called  this  the  magne-crys- 
tallic  force. 

Pliicker  infers  from  these  phenomena  that  a  definite  relation 
exists  between  the  ultimate  form  of  the  particles  of  matter 
and  their  magnetic  behavior.  The  subject  may  be  regarded 
as  yet  somewhat  obscure.  (See  Diamagnetic  Polarity.) 

Magnet. — A  body  possessing  the  power  of  attracting  the 
unlike  poles  of  another  magnet  or  repelling  the  like  poles  ;  or 
of  attracting  readily  magnetizable  bodies  like  iron  filings  to 
either  pole. 

A  body  possessing  a  magnetic  field. — (See  Field,  Magnetic.) 

The  lines  of  force  are  assumed  to  pass  through  the  magnetic 

field  out  at  the  north  pole  and  in  at  the  south  pole.     All  lines  of 

force  form  closed  magnetic  circuits.      If  a  magnetizable  body 

is  brought  into  a  magnetic  field,  the  lines  of  magnetic  force 


WORDS,  TERMS  AND  PHRASES.  395 

are  concentrated  on  it  and  pass  through  it.  The  body  there- 
fore becomes  magnetic.  The  intensity  of  the  resulting 
magnetism  depends  on  the  number  of  lines  of  force  that  pass 
through'  the  body,  and  the  polarity  on  the  direction  in  which 
they  pass  through  it. 

Magnet,  Anomalous A  magnet  which  pos- 
sesses more  than  two  poles. — (See  Anomalous  Magnet.) 

Magnet,  Artificial  — A  magnet  produced  by 

induction  from  another  magnet,  or  from  an  electric  current. 

Any  magnet  not  found  in  nature  is  called  an  artificial 
magnet. 

Magnet,  Bell  Shaped  —  —A  modification  of  a 

horseshoe  shaped  magnet  in  which  the  approached  poles  are 
semi-annular  in  shape,  and  form  a  split  tube. 

Bell  magnets  are  used  in  many  gal  vanometei's,  because  they 
can  be  readily  dampened  by  surrounding  them  by  a  mass  of 
copper.  The  needle  in  its  motion  produces  currents  that 
tend  to  oppose  and  therefore  to  stop  its  motion.  (See  Lenz's 
Law.) 

Magnet  Coils. — The  coils  of  insulated  wire  surrounding 
the  core  of  an  electro  magnet,  and  through  which  the  mag- 
netizing current  is  passed. — (See  Magnetism,  Ampere's  Theory 
of.  Dynamo  Electric  Machine,  Field  Magnets.) 

Magnet,  Compensating  —  —A  magnet  placed 

over  a  magnetic  needle,  generally  over  the  magnetic  needle 
of  a  galvanometer,  for  the  purpose  of  varying  the  direction 
and  intensity  of  the  magnetic  force  of  the  earth  on  the 
needle.— (See  Galvanometer,  Reflecting.) 

A  magnet,  called  a  compensating  magnet,  is  sometimes  placed 
on  a  ship,  near  the  compass  needle,  for  the  purpose  of  neutral- 
izing the  local  variation  produced  on  the  compass  needle  by 
the  magnetism  of  the  ship. 


A  DICTIONARY  OP  ELECTRICAL 


Magnet,  Compound 


—A  number  of  single 
magnets,  placed  parallel  and  with  their  similar  poles  facing 
one  another,  as  shown  in  Fig.  274. 

Compound  magnets  are  stronger  in  proportion  to  their 
weight  than  single  magnets. 

Magnet,  Electro —A  magnet  produced  by  the 

passage  of  an  electric  current  around  a  core  of  soft  iron. — (See 
Electro-Magnet. ) 

Magnet,  Hor§eghoe (See 

Horseshoe  Magnet.) 

Magnet,  Keeper  of (See 

Keeper  of  Magnet.) 

Magnet,    Permanent —A 

magnet  of  hardened  steel  or  other  sub- 
stance which  retains  its  magnetism  for  a 
long  time  after  being  magnetized. 

A  permanent  magnet  is  distinguished, 
in  this  respect,  from  a  temporary  magnet 
of  soft  iron  which  loses  its  magnetization 
very  shortly  after  being  taken  from  the 
magnetizing  field. 

Magnet,  Portative  Power  of — 

The  lifting  power  of  a  magnet. 

The  port  at  ive,  or  lifting  power  of  a  magnet,  depends  on  the 
form  of  the  magnet,  as  well  as  on  its  strength.  A  horseshoe 
magnet,  for  example,  will  lift  a  much  greater  weight  than 
the  same  magnet  if  in  the  form  of  a  straight  bar. 

This  is  due  not  only  to  the  mutual  action  of  the  approached 
poles,  but  also  to  the  decreased  resistance  of  the  magnetic 
circuit,  and  to  the  greater  number  of  lines  of  magnetic  force 
that  pass  through  the  armature. 

The  portative  power  increases  as  the  area  of  contact  in- 
creases. 

Magnet,  Receiving or  Relay. — (See  Relay.) 


WORDS,  TEEMS  AND  PHRASES.  397 

Magnet,  Simple  ---  A  single  magnetized  bar. 

Magnet,  Solcnoidal  --  -  —A  long,  thin,  uniformly 
magnetized  straight  bar  of  steel,  with  its  poles  at  its  extremi- 
ties, that  acts  on  external  objects  as  if  equal  and  opposite  quan- 
ties  of  magnetism  were  collected  at  its  extremities. 

It  derives  its  name  solenoidal,  from  the  similarity  between 
its  action  and  that  of  a  solenoid.  Unless  very  carefully  mag- 
netized a  magnet  will  not  act  as  a  solenoidal  magnet.  (See 
Electro-Magnet.  Solenoidal  Distribution  of  Magnetism.) 


lar  --  or  Iron-Clad  Magnet.— 

A  form  of  horseshoe  magnet  in  which  one  pole  is  brought 
near  the  opposite  pole  by  a  hollow  cylinder  or  tube,  which  is 
placed  in  contact  with  one  of  the  magnetic  poles,  so  as  to 
completely  surround  the  other,  except  in  the  plane  of  cross 
section  of  that  pole. 

There  is  thus  obtained  a  magnet,  with  two  concentric  poles, 
one  solid  and  one  annular,  the  portative  power  of  which  is 
much  greater  than  that  of  a  horseshoe  magnet  of  equal  di- 
mensions. 

Magnetic  Attraction.  —  (See  Attraction,  Magnetic.) 
Magnetic  Axi§.—  (See  Axis,  Magnetic.) 
Magnetic  Azimuth.  —  (See  Azimuth,  Magnetic.) 
Magnetic  Battery.—  (See  Battery,  Magnetic.) 
Magnetic  Bridge.—  fSee  Bridge,   Magnetic.) 
Magnetic  Circuit.—  (See  Circuit,  Magnetic.) 
Magnetic  Couple.—  (See  Couple,  Magnetic.) 

Magnetic  Curves.—  Curved  lines,  formed  by  sprinkling 
iron  filings  on  a  sheet  of  paper  or  glass  held  in  the  field  of  a 
magnet,  and  gently  tapping  the  same  so  as  to  permit  the  fil- 
ings to  arrange  themselves  in  the  direction  of  the  lines  of 
magnetic  force.  (See  Figures,  Magnetic.) 


A  DICTIONARY  OF  ELECTRICAL 

Magnetic  Declination.— The  angular  deviation  of  the 
magnetic  needle  to  the  east  or  west  of  the  true  geographical 
north.  (See  Needle,  Declination  of.  Declination  Chart.) 

Magnetic  Density. — (See  Density,  Magnetic.) 
Magrnetic  Dip.— (See  Dip,  Magnetic.) 
Magnetic  Explorer. — (See  Explorer,  Magnetic.) 

Magnetic  Field. — The  atmosphere  of  magnetic  influence 
which  surrounds  the  poles  of  a  magnet. 

Any  space  traversed  by  lines  of  magnetic  force,  forms  a 
magnetic  field.'  (See  Field,  Magnetic.) 

Magnetic  Figures.— (See  Figures  Magnetic.  Field,  Mag- 
netic.) 

Magnetic  Filament.— A  polarized  line  or  chain  of  ulti- 
mate magnetic  particles.  (See  Filament,  Magnetic.) 

Magnetic  Force.— The  force  which  causes  magnetic  at- 
tractions and  repulsions. 

Magnetic  Inclination. — The  angular  deviation  from 
a  horizontal  position  of  a  freely  suspended  magnetic  needle. 
(See  Dip  of  Needle.  Inclination  Chart.) 

Magnetic  Induction. — The  magnetization  of  magnetiz- 
able substances  by  bringing  them  into  a  magnetic  field.  (See 
Induction,  Magnetic.) 

Magnetic  Inertia. — (See  Inertia,  Magnetic.  Lag, 
Magnetic.) 

Magnetic  Intensity. — (See  Intensity  of  Magnetiza- 
tion.) 

Magnetic  Lag. — (See  Lag,  Magnetic.) 

Magnetic  Leakage. — Useless  dissipation  of  lines  of 
magnetic  force  outside  that  portion  of  the  field  of  a  dynamo 
electric  machine  through  which  the  armature  moves. 

Magnetic  leakage  will  result  in  a  low  efficiency  of  the  dyna- 
mo. (See  Coefficient,  Economic  of  Dynamo.) 


WORDS,  TERMS  AND  PHRASES.  399 

Magnetic  L-ines  of  Force. — (See  Lines  of  Force,  Mag- 
netic.) 

Magnetic  Masses. — (See  Masses,  Magnetic.) 

magnetic  Memory. — A  term  proposed  by  J.  A.  Fleming 
for  coercive  force. 

Soft  iron  has  but  a  feeble  memory  of  its  past  magnetization. 

Magnetic  Meridian. — The  magnetic  meridian  of  any 
place  is  the  meridian  which  passes  through  the  poles  of  a  mag- 
netic needle,  when  in  a  position  of  rest  under  the  free  influence 
of  the  earth's  magnetism  at  that  place. 

The  plane  of  the  magnetic  meridian  of  a  place  is  a  vertical 
plane  passing  through  the  poles  of  a  magnetic  needle  in  a 
position  of  rest  under  the  free  influence  of  the  earth's  mag- 
netism at  that  place. 

Magnetic  Moment. — The  magnetic  moment  of  a  mag- 
netic needle  is  the  product  of  one  of  the  two  forces  of  the 
directive  couple,  multiplied  by  the  perpendicular  distance  be- 
tween the  directions  of  these  forces  ;  or,  in  other  words,  the 
moment  of  a  magnet  is  equal  to  its  length  multiplied  by  the 
intensity  of  the  magnetism  of  one  of  its  poles.  (See  Couple, 
Magnetic). 

Magnetic  Observatory. — (See  Observatory,  Magnetic.) 

Magnetic  Permeability .— Conductibility  for  lines  of 
magnetic  force. 

Iron  is  a  substance  which  possesses  great  magnetic  permea- 
bility. When  placed  in  a  magnetic  field  the  lines  of  force 
are  concentrated  on  and  readily  pass  through  its  mass,  or,  in 
other  words,  its  magnetic  resistance  is  low.  All  paramag- 
netic bodies,  have  a  high  magnetic  permeability.  (See  Par- 
amagnetic) 

Magnetic  Poles,  False (See  False  Poles,  Mag- 
netic.) 

Magnetic  Reluctance. — A  term  recently  proposed  in 
place  of  magnetic  resistance,  to  express  the  resistance  offered 


400  A  DICTIONARY   OF  ELECTRICAL 

by  a  medium  to  the  passage  through  its  mass  of  the  lines  of 
magnetic  force. 

magnetism,  Residual The  small  amount  of 

magnetism  retained  by  soft  iron  when  removed  from  a  mag- 
netizing field. 

Magnetic  Resistance.— Resistance  offered  by  a  medium 
to  the  passage  of  the  lines  of  magnetic  force  through  it. 

The  magnetic  resistance  of  the  circuit  of  the  lines  of  force  is 
reduced  by  forming  the  circuit  of  a  medium  having  a  high 
magnetic  permeability,  such  as  softiron.  This  is  accomplished 
by  the  armature  or  keeper  of  a  magnet,  or  by  the  iron  in  an 
ironclad  magnet.  (See  Iron- Clad  Magnet.) 

Magnetic  Retentivity.— (See  Retentivity,  Magnetic.) 

Magnetic  Saturation.— The  condition  of  iron,  or  other 
paramagnetic  substance,  when  its  intensity  of  magnetization  is 
so  great  that  it  fails  to  be  further  magnetized  by  any  magnetic 
force  however  great. 

When  the  core  of  an  electro-magnet  is  saturated  by  the 
passage  of  an  electric  current,  the  only  further  increase  of  its 
magnetization  that  is  possible,  is  that  due  to  the  magnetic 
field  of  the  increased  current  which  may  be  sent  through  its 
coils.  This  is  comparatively  insignificant. 

A  magnet  is  sometimes  said  to  be  super-saturated,  that  is, 
to  have  received  more  magnetism  than  it  can  retain  for  any 
considerable  time  after  its  magnetization. 

Magnetic  Screen,  or  Shield.— A  hollow  box  whose 
sides  are  made  of  thick  iron,  placed  around  a  magnet  or  other 
body  so  as  to  cut  it  off  or  screen  it  from  any  magnetic  field 
external  to  the  box. 

Magnetic  screens  are  placed  around  delicate  galvanometers 
to  avoid  any  variations  in  their  field  due  to  extraneous  masses 
of  iron,  or  neighboring  magnets.  They  are  also  sometimes 
placed  around  watches  to  shield  or  screen  the  works  from  the 
effects  of  magnetism. 


WORDS,  TERMS  AND  PHRASES.  401 

To  act  effectively,  when  the  external  fields  are  at  all  power- 
ful, magnetic  screens  must  be  made  of  thick  iron.  They  differ 
in  this  respect  from  electrostatic  shields,  which  will  afford 
protection  against  electrostatic  charges  although  they  may  be 
but  mere  films.  (See  Shields,  Electrostatic.) 

Magnetic  Shells.— A  sheet  or  layer  consisting  of  mag- 
netic particles,  all  of  whose  north  poles  are  situated  in  one  of 
the  flat  surfaces  of  the  sheet,  and  the  sovith  poles  in  the  oppo- 
site surface.  (See  Shell,  Magnetic.  Lamellar  Distribution  of 
Magnetism.) 

Magnetic  Solenoids. — A  spiral  coil  of  wire  which  acts 
like  a  magnet  when  an  electric  current  passes  through  it.  (See 
Solenoids,  Electro-Magnetic.) 

Magnetic  Sounds.— Faint  clicks  heard  on  the  magneti- 
zation of  a  readily  magnetizable  substance. 

One  of  the  earlier  forms  of  Eeis'  telephone  operated  by 
means  of  a  rapid  succession  of  these  faint,  magnetic  sounds. 

Magnetic  Storms. — Sudden,  but  small  and  irregular 
variations  in  the  intensity  of  the  earth's  magnetism  that 
simultaneously  affect  all  parts  of  the  earth. 

Magnetic  storms  have  been  observed  to  accompany  auroral 
displays,  and  to  be  coincident  with  the  occurrence  of  sun 
spots,  or  unusual  outbursts  of  solar  activity. 

Magnetic  Susceptibility.— The  relation  which  exists  be- 
tween the  strength  of  the  magnetizing  field  and  that  of  the 
magnetized  body,  or  the  intensity  of  the  magnetism  induced, 
divided  by  the  intensity  of  the  inducing  field. 

When  the  inducing  field  has  unit  strength  of  magnetiza- 
tion the  magnetic  susceptibility  will  measure  directly  the 
strength  of  the  magnetization. 

When  a  bar  of  iron  is  placed  in  a  magnetic  field,  it  is 
threaded  by  the  lines  of  magnetic  force,  and  thus  becomes 
magnetized  by  induction,  This  induction  will  necessarily 


402  A  DICTIONARY  OF  ELECTRICAL 

depend  both  on  the  number  of  lines  of  force  in  the  magnet- 
izing field,  and  on  the  magnetic  permeability  of  the  magnet- 
ized body ;  or,  in  other  words,  the  induction  is  equal  to  the 
product  of  the  intensity  of  the  magnetizing  field  and  the 
magnetic  permeability  of  the  body  in  which  the  induction 
occurs. 

magnetic  Variations. — Variations  in  the  value  of  the 
magnetic  declination,or  inclination,  that  occur  simultaneously 
over  all  parts  of  the  earth. 

These  variations  are : 

(1)  Secular,- or  those  occurring  at  great  cycles  of  time. 

(2)  Annual,  or  those  occurring  at  different  seasons  of  the 
year. 

(3)  Diurnal,   or  those  occurring  at  different  hours  of  the 
day,  and, 

(4)  Irregular,  or  those  accompanying  magnetic  storms.  The 
first  three  are  periodical ;  the  last  is  irregular.     (See  Angle  of 
Declination.     Variation  Chart.    Inclination  Chart.) 

magnetite. — Magnetic  oxide  of  iron,  or  Fes  O4. 

Lodestone  consists  of  pieces  of  magnetized  magnetite. 

Magneto-Electricity.— Electricity  produced  by  the  mo- 
tion of  magnets  past  conductors,  or  of  conductors  past  mag- 
nets. 

Magneto-Electric  Call  Bell.— An  electric  call  bell 
operated  by  currents  produced  by  the  motion  of  a  coil  of  wire 
before  the  poles  of  a  permanent  magnet. 

Magneto-Electric  Induction.— Electric  induction  pro- 
duced by  the  motion  of  a  conductor  past  a  permanent  magnet, 
or  vice  versa.  (See  Induction,  Electro  Magnetic.) 

Magneto-Electric  Machine.— A  dynamo  in  which 
currents  are  produced  by  the  motion  of  armature  coils  past 
permanent  magnets.  (See  Dynamo  Electric  Machine. ) 

Magnctograph,  or  Self-Recording  Magnetome- 
ter.— A  self-recording  apparatus  by  means  of  which  the  daily 


WORDS,  TERMS  AND  PHRASES.  403 

and  hourly  variations  of  the  magnetic  needle  are  continuously 
registered. 

The  magnetograph,  as  employed  in  the  observatory  at  Kew, 
consists  essentially  of  a  photographic  record  of  a  spot  of  light 
reflected  from  a  mirror  attached  to  the  needle  whose  varia- 
tions are  to  be  record- 
ed.  The  photographic 
record  is  received  on 
a  strip  of  sensitized 
paper,  maintained  in 
uniform  and  continu- 
ous motion  by  means 
of  suitable  clockwork. 
The  record  so  obtained 
is  called  a  magneto- 
graph. 

magiietoinct  e  r . 

—  An  apparatus  for 
the  measurement  of 
magnetic  force  by  the 
torsion  balance. 

The  principles  of 
the  operation  of  the 
magnetometer  are  the 
same  as  those  of  the 
torsion  balance.  (See 
Balance,  Coulomb's 
Torsion.)  A  mag- 
net N  S,  Fig.  275,  is 
suspended  by  a  single 
wire,  ;ind  the  magnet 
N,  whose  strength  is  to  be  measured  is  introduced  in  an  open- 
ing at  the  top  of  the  glass  cage,  in  place  of  the  proof  plane 
which  is  used  when  the  apparatus  is  employed  for  measuring 
the  force  of  electrostatic  attraction  and  repulsion. 


404  A  DICTIONARY  OF  ELECTRICAL 

In  delicate  magnetometers,  the  construction  of  which  differs 
considerably  from  the  form  shown  in  Fig.  275,  the  deflection 
of  the  magnet  is  measured  by  a  beam  of  light  reflected  from  a 
mirror  attached  to  the  axis  of  suspension. 

Magneto-Optic  Rotation.— The  rotation  of  the  plane 
of  polarization  of  a  beam  of  light  on  its  passage  through  a 
transparent  medium  placed  in  a  strong  magnetic  field, 
which  medium  only  possesses  such  properties  while  in  the 
field. 

In  a  ray  of  ordinary  light  the  vibrations  of  the  ether  parti- 
cles ai-eat  right  angles  to  the  direction  of  the  ray,  or  to  the 
direction  in  which  the  light  is  moving.  Successive  ether 
particles  that  lie  along  the  path  of  the  ray,  do  not,  however, 
perform  their  vibrations  in  the  same  plane.  Each  successive 
particle  moves  in  a  plane  which,  though  at  right  angles 
to  the  ray,  is  slig'htly  inclined  to  the  neighboring  particle. 

The  motion  of  the  particles  therefore,  would  describe  a 
screw-like  path  through  space.  Under  certain  circumstances, 
all  the  ether  particles  may  be  caused  to  move  in  planes  that 
are  parallel  to  one  another.  Such  a  beam  of  light  is  called  a 
plane  polarized  beam. 

A  plane  polarized  beam,  when  passed  through  many  trans- 
parent substances,  will  have  its  ether  particles  vibrating  in 
the  same  plane  when  it  emerges  from  the  medium,  as  it  had 
before  it  entered.  Other  substances  possess  the  property  of 
rotating  or  turning  the  plane  of  polarization  of  the  light  to 
the  right  or  to  the  left.  This  property  is  called  respectively 
right-handed  rotary  polarization,  and  left-handed  rotary 
polarization. 

Many  substances  that  ordinarily  possess  no  power  of  rotary 
polarization  acquire  this  power  when  placed  in  a  magnetic 
field.  This  property  of  a  magnetic  field  was  discovered  by 
Faraday.  The  effect  is  to  be  ascribed  to  the  strain  produced 
in  the  transparent  medium  by  the  stress  of  the  magnetic  field. 
Jt  may  be  caused  in  solid  bodies  by  mechanical  forge. 


WORDS,  TERMS  AND  PHRASES.  405 

The  apparatus  for  demonstrating  the  rotation  of  the  plane 
of  polarization  by  a  magnetic  field  is  shown  in  Fig.  276. 

A  powerful  electro-magnet  M,  N,  is  provided  with  a  hollow 
core.  The  substance  c,  is  placed  in  the  field  thus  produced 
by  the  approached  poles,  and  its  action  on  the  light  of  a 
lamp,  placed  opposite  at  /,  is  observed  by  suitable  apparatus 
at  a. 

Magnetophone. — An  apparatus  for  measuring  the  num- 
ber of  breaks  or  interruptions  of  a  circuit  by  the  pitch  of  the 
musical  note  heard  in  an  electro-magnetic  telephone  placed  in 
such  circuit.  (See  Telephone,  Electro-Magnetic.) 


fig.  276. 

A  similar  apparatus  is  useful  in  studying  the  distribution  of 
the  magnetic  field  of  a  dynamo  electric  machine.  In  this  case, 
a  small  thin  coil  of  insulated  wire  is  held  in  the  different 
regions  around  the  machine,  while  the  telephone  is  held  to  the 
ear  of  the  observer.  Magnetic  leakage,  or  useless  dissipation  of 
linesof  magnetic  force  outside  the  field  proper  of  the  machine, 
is  at  once  rendered  manifest  by  the  musical  note  caused  by 
variations  in  the  intensity  of  the  field. 

Since  the  intensity  of  the  note  heard  will  vary  according  to 


406 


A  blCTIONAKY  OF  ELECTRICAL 


the  intensity  of  the  field,  and  also  according  to  the  position  in 
which  the  coil  is  held,  such  a  coil  becomes  a  magnetic  explorer, 
and  by  its  use  the  distribution  and  varying  intensity  of  an 
irregular  field  can  be  ascertained.  Its  use  is  especially  advan- 
tageous in  proportioning  dynamo-electric  machines,  and  elec- 
tric motors. 

Magnetism. — That  branch  of  science  which  treats  of  the 
properties  of  a  magnetic  field.  (See  Field,  Magnetic.) 

Magnetism,  Ampere's  Theory  of.— A  theory  or  hypo- 
thesis proposed  to  account  for  the  cause  of  magnetism  by 
the  presence  of  electric  currents  in  the  ultimate  particles  of 
matter. 


This  theory  assumes . 

(1)  That  the  ultimate  particles  of  all  magnetizable  bodies 
have  closed  electric  circuits  in  which  electric  currents  are  con- 
tinually flowing. 

(2)  That  in  an  unmagnetized  body  these  circuits  neutralize 
one  another  because  they  have  different  directions. 

(3)  That  the  act  of  magnetization  consists  in  such  a  polariza- 
tion of  the  particles  as  will  cause  these  currents  to  flow  in  one 
and  the  same  direction,  magnetic  saturation  being  reached 
when  all  the  separate  currents  are  parallel  to  one  another. 

(4)  That  the  coercive  force  is  due  to  the  resistance  these 
circuits  offer  to  a  change  in  the  direction  of  their  planes. 


WORDS,  TERMS  AND  PHRASES.  407 

Figs.  277  and  278,  show  the  circular  paths  of  some  of  these 
circuits.  Fig.  277  shows  the  assumed  condition  of  an  unmag- 
netized  bar.  Fig.  278  the  assumed  condition  of  a  magnetized 
bar. 

A  careful  inspection  of  the  figures  will  show  that  in  a  magne- 
tized bar  all  the  separate  currents  flow  in  the  same  direction. 
All  tJte  circuits  except  those  on  the  extreme  edge  of  the  bar 
will,  therefore,  have  the  currents  flowing  in  them  in  opposite 
directions  to  that  in  their  neighboring  circuits,  and,  therefore* 
will  neutralize  one  another.  There  will  remain,however,  a 
current  in  a  circuit  on  the  outside  of  the  bar,  which  must 
therefore  be  regarded  as  the  magnetizing  circuit. 

Guided  by  these  considerations,  Ampere  produced  a  coil  of 
wire,  called  a  solenoid,  which  is  the  equivalent  of  the  magnetiz- 
ing circuit  assumed  by  his  theory. 

It  therefore  follows  that  an  electric  current  sent  through  a 
coil  of  insulated  wire  surrounding  a  rod  or  bar  of  soft  iron,  or 
other  readily  magnetizable  material,  will  make  the  same  a 
magnet.  A  magnet  so  produced  is  called  an  electro-magnet. 
(See  Electro-Magnet.) 

The  magnetizing  coil  is  called  a  helix  or  solenoid.  (See 
Solenoid,  Electro-Magnetic.) 

The  polarity  of  the  magnet  depends  on  the  direction  of  the 
current,  or  on  the  direction  of  winding  of  the  helix  or  sole- 
noid. (See  Solenoids,  Sinistrorsal  and  Dextrorsal.) 

Magnetism,  Electro  —  •  —Magnetism  produced 

be  means  of  electric  currents. 

The  discovery  of  Oersted,  in  1820,  of  the  action  of  an  elec- 
tric current  on  a  magnetic  needle,  was  almost  immediately 
followed  by  the  simultaneous  and  independent  discoveries  of 
Arago  and  Davy,  of  the  method  of  magnetizing  iron  by  the 
passage  of  an  electric  current  around  it. 

These  observations  were  first  reduced  to  a  theory  by  Am- 
p6re.  (See  Magnetism,  Ampere's  Theory  of.  Electro-Mag- 
net.) 


408  A  DICTIONARY  OF  ELECTRICAL 

magnetism,  I  lug  lies'  Theory  of A  theory  pro- 
pounded by  Hughes  to  account  for  the  phenomena  of  magnet- 
ism apart  from  the  presence  of  electric  currents . 

Hughes'  theory,  or,  more  strictly  speaking,  hypothesis  of 
magnetism,  though  very  similar  to  that  of  Ampere,  does  not 
assume  th»  improbable   condition   of  a   constantly  flowing 
electric  current. 
Hughes'  hypothesis  assumes : 

(1)  That  the  molecules  of  matter,  and  probably  even  the 

n  s  K     s  .*L  s  atoms,  possess  naturally  op- 

w^***""  ""*  «S^s  posite  magnetic  polarities 

^  *P       which  are  respectively  -f-  and 

*/  \n   -,orN.andS. 

I  \s       (2)  That    these    molecules, 

In    when    arranged  in   closed 

^  *  s      chains  or  circuits,  are  capable 

s^^  ^^  ^  of  neutralizing  one  another  so 

n  s  n  s    n  s    r'  far  as  external  action  is  con- 

Fig-  279.  cerned. 

Two  such  arrangements  or  groupings  are  shown  in  Figs. 
279  and  280.  It  will  be  observed  that  the  magnetic  chain 
or  circuit  is  complete,  and  that,  therefore,  the  substance  can 
possess  no  magnetic  properties  so  far  as  external  action  is 
concerned. 


-HUH  IIIIHfl  IHIU 

s  n    s  n     s  n     s  .n     s  n     s  n     s  n    s  -n    s  n    &  n 

Fig.  280. 

(3)  That  the  act  of  magnetization  consists  in  such  a  rota- 
tion of  the  molecules,  that  a  polarization  of  the  substance  is 
effected ;  that  is,  the  molecules  are  rotated  on  their  axes  so 
that  one  set  of  poles  tend  to  point  in  one  direction,  and  the 
other  set  of  poles  in  the  opposite  direction. 


WORDS,  TERMS  AND  PHRASES.  400 

Partial  magnetization  consists  in  partial  polarization.  Mag- 
netic saturation  is  reached  when  the  polarization  is  complete. 
(See  Magnetic  Saturation.) 

Coercive  force  is  the  resistance  the  body  offers  to  the  polariza- 
tion or  rotation  of  its  molecules.  (See  Coercive  Force.) 

Hughes'  hypothesis  of  magnetism  would  appear  to  be 
strengthened  by  the  following  facts : 

(1)  A    bar    of  steel    or  iron  is    sensibly  elongated  on  be- 
ing magnetized.      This  would  naturally  result  if  the  mole- 
cules be  supposed  to  be  longer  in  one  direction  than  in  any 
other. 

(2)  A  tube,  furnished  at  its  ends  with  plates  of  flat  glass  and 
filled  with  water  containing  finely  divided  magnetic  oxide  of 
iron,  is  nearly  opaque  to  light  when  unmagnetized,  but  will 
permit  some  light  to  pass  through  it  when  magnetized. 

(3)  A  magnet,  if  cut  at  its  neutral  point,  will  possess  op- 
posite polarities  at  the  cut  ends ;  and  no  matter  to  what  ex- 
tent this  subdivision  is  carried  the  particles  will  still  possess 
opposite  polarities. 

These  facts  are,  however,  also  explained  by  Ampere's  hy- 
pothesis of  magnetism,  with,  however,  the  improbable  as- 
sumption of  a  constantly  flowing  current  in  each  molecule. 

Magnetism,    Lamellar (See  Lamellar  Magne- 

tum.) 

Magnetism,  Solenoidal  Distribution  of —      —A 

term  sometimes  applied  to  a  distribution  of  magnetism  in  a  bar 
such  that  the  magnetized  particles  are  arranged  with  their 
poles  in  the  direction  of  the  length  of  the  bar,  in  contra-dis- 
tinction  to  a  lamellar  distribution.  (See  Lamellar  Distribu- 
tion of  Magnetism.) 

Magnetization,  Coefficient  of (See  Coefficient 

of  Magnetization.) 

Magnetization,    Critical     Current    of (See 

Critical  Current  of  Magnetization.) 


410  A  DICTIONARY  OP  ELECTRICAL 

Magnetization,  II  el  hods  of Magneti- 
zation effected  either  by  induction  from  another  magnet,  or 
by  means  of  induction  by  an  electric  current. 

The  substance  to  be  magnetized  is  brought  into  a  magnetic 
field,  so  that  the  lines  of  magnetic  force  pass  through  it.  All 
methods  of  magnetization  may  be  divided  into  methods  of 
touch,  and  magnetization  by  the  electric  current. 

Mains,  Electric The  principal  conductors  in  any 

system  of  electric  distribution.  (See  Leads,  Electric.) 

Mallet,  Electro-Magnetic (See  Electro-Mag- 
netic Mallet.} 

Manipulator,  Breguet's (See  Needle  Tele- 
graph.) 

Manometer. — An  apparatus  for  measuring  the  tension  or 
pressure  of  gases. 

Manometers  are  either  mercurial  or  metallic.  They  meas- 
ure the  pressure  of  gases  either  in  atmospheres,  i.  e.,  in  mul- 
tiples or  decimals  of  15  pounds  to  the  square  inch,  or  in  inches 
of  mercury. 

Marine  Oalvanometer. — (See  Galvanometer,  Marine.) 

Mariners'  Compass.— (See  Compass,  Azimuth.) 

Marked  Pole  of  a  Magnet.— The  pole  of  a  magnet 
that  points  approximately  to  the  geographical  north. 

If  the  pole  of  the  magnet  that  points  to  the  geographical 
north  be  in  reality  the  north  pole  of  the  magnet,  then  the 
earth's  magnetic  pole  in  the  Northern  Hemisphere  is  of  south 
magnetic- polarity.  In  the  United  States,  and  Europe  gener- 
ally, this  is  regarded  to  be  the  fact. 

The  French,  however,  call  the  pole  of  the  needle  that  points 
to  the  earth's  geographical  north,  the  south  or  austral  pole. 
In  America  and  England  it  is  called  the  north  pole,  the  marked 
pole,  or  the  north-seeking  pole,  and  the  Northern  Hemisphere 
is  assumed  to  possess  south  magnetic  polarity.  (See  Aus- 
tral and  Boreal  Poles.) 


WORDS,  TERMS  AND  PHRASES.  411 

19Iarker§. — Green  flags,  or  signal  lights,  displayed  on  the 
ends  of  trains,  in  systems  of  block  railway  signalling  in  order 
to  avoid  accidents  from  trains  breaking  in  two.  (See  Block 
Signals,  System  of.) 

Mass. — The  qviantity  of  matter  contained  in  a  body. 

Mass  must  be  carefully  distinguished  from  weight.  The 
weight  of  a  given  quantity  of  matter  depends  on  the  attraction 
which  the  earth  possesses  for  it,  and  this,  on  the  earth's  sur- 
face, varies  with  the  latitude,  being  greatest  at  the  poles,  and 
least  at  the  equator.  It  also  varies  with  different  elevations 
above  the  level  of  the  sea.  The  mass,  however,  is  the  same 
under  all  circumstances. 

Mass,  Magnetic  —  —Such  a  quantity  of  magne- 

tism, that  at  unit  distance  produces  an  action  equal  to  unit 
force. 

Mass,  Unit  of The  quantity  of  matter  which 

under  certain  conditions  will  balance  the  weight  of  a  standard 
gramme  or  pound. 

Masses,  Eleetrie  —  —A  mathematical  conception 
for  such  quantities  of  electricity  that  at  unit  distance  will 
produce  an  attraction  or  repulsion  equal  to  unit  force. 

Electrical  masses  are  assumed  to  be  equal  when  they  pro- 
duce on  two  identical  bodies  of  small  dimensions  charges  of 
the  same  electric  force. 

Master-Clock.— The  central  or  controlling  clock  in  a  sys- 
tem of  electric  time  distribution,  from  which  the  time  is 
transmitted  to  the  secondary  clocks  in  the  circuit.  (See 
Clocks,  Electric.) 

Matter.— That  which  occupies  space  and  prevents  other 
matter  from  simultaneously  occupying  the  same  space. 

Matter  is  composed  of  atoms,  which  unite  to  form  molecules. 
(See  Atoms.  Molecules.) 

Matter,  Elementary (See  Element.) 


412  A  DICTIONARY  OP  ELECTRICAL 

matter,    Radiant,    or     lJltra-Gaseou§ A 

term  proposed  by  Crookes  for  the  peculiar  condition  of  the 
matter  which  constitutes  the  residual  atmospheres  of  high 
vacua. 

The  peculiar  properties  of  radiant  matter  are  seen  in  the 
mechanical  effects  of  the  localized  pressure  produced  when 
such  residual  atmospheres  are  locally  heated  or  electrified. 

In  Crookes'  Radiometer,  vanes  of  mica,  silvered  on  one  face 
and  covered  with  lampblack  on  the  opposite  face,  are  sup- 
ported on  a  vertical  axis,  so  as  to  be  capable  of  rotation  and 
placed  in  a  glass  vessel  in  which  a  high  vacuum  is  maintained. 
On  exposing  the  instrument  to  the  radiation  from  a  candle  or 
gas  flame,  a  rapid  rotation  takes  place. 

The  explanation  is  as  follows  :  The  lampblack  covered  sur- 
faces absorb  the  radiant  heat,  and  becoming  heated  the 
molecules  of  gas  in  the  residual  atmosphere  are  shot  violently 
from  these  heated  surfaces,  and  by  their  reaction  drive  the 
vanes  around  in  the  opposite  direction  to  that  from  which 
they  are  thrown  off.  The  molecules  are  also  shot  off  from  the 
silvered  surfaces,  but,  as  these  are  cooler,  the  effect  is  not  as 
great  as  at  the  blackened  surfaces. 

In  a  gas,  at  ordinary  pressure,  the  heated  surfaces  are  also 
bombarded  by  other  molecules  of  the  g-as,  but  in  high  vacua  the 
mean  free  path  of  the  molecules  is  such  that  there  is  no  inter- 
ference, a  Crookes1  layer  existing  between  the  vanes  and  the 
walls  of  the  glass  vessel.  (See  Layer,  Crookes'.) 

When  a  Crookes'  tube  is  furnished  with  suitable  electrodes, 
and  electric  discharges  are  sent  through  it  between  these 
electrodes,  a  stream  of  molecules  is  thrown  off  in  straigr  t 
lines  from  the  surface  of  the  negative  electrode. 

Some  of  the  effects  of  this  molecular  bombardment  are  seen 
by  the  use  of  the  apparatus  shown  in  Fig.  281.  When  the 
positive  and  negative  terminals  are  arranged  as  shown,  the 
paths  of  the  molecular  streams  are  seen  as  luminous  streams 
whose  directions  are  those  shown  in  the  figures. 


WORDS,  TERMS    AND   PHRASES. 


413 


The  figure  on  the  left  shows  the  path  taken  in  a  low  vacuum. 
Streams  pass  from  the  negative  electrode  to  each  of  the  pos- 
itive electrodes. 

The  figure  on  the  right  shows  the  discharge  in  a  high 
vacuum.  Here  the  streams  pass  off  at  right  angles  to  the  face 


Fig.  281. 

of  the  negative  electrode,  and  proceed  therefrom  in  straight 
lines,  independently  of  the  position  of  the  positive  electrode. 
Since,  therefore,  the  negative  electrode  at  a,  is  in  the  shape  of 
a  concave  mirror,  the  luminous  particles  converge  to  a  focus 
near  the  centre  of  the  glass  vessel,  and  then  diverge  to  the 
opposite  wall, 


414 


A  DICTIONARY  OF  ELECTRICAL, 


Refractory  substances  placed  at  such  a  focus  of  molecular 
bombardment,  as  shown  in  Fig.  282,  are  rendered  incan- 
descent. 

In  a  similar  manner,  phosphorescent  substances  exposed  to 
such  molecular  streams  emit  a  beautiful  phosphorescent  light. 
(See  Phosphorescence,  Electric.) 

Measurements,  Electric Determinations  of 

the  values  of  the  E.  M.  F.,  resist- 
ance, current,  capacity,  energy, 
etc.,  in  any  electric  circuit. 

Electric  measurements  may  be 
either  qualitative  or  quantitative. 

mechanical  Equivalent  of 
Heat. — The  amount  of  mechanical 
energy  converted  into  heat  that 
would  be  required  to  raise  the  tem- 
pei'ature  of  one  pound  of  water  1°  F. 

The  mechanical  equivalence  be- 
tween the  energy  expended  and  the 
heat  produced. 

Joule's  experiments,  the  results  of 
which  are  generally  accepted,  gave 
772  foot  pounds  as  the  energy  equiv- 
alent to  that  expended  in  raising 
the  temperature  of  one  pound  of 
water  1°  F. 

Media,  Anisotropic 

(See  Anisotropic  Media.) 
Meg  or  Mega  (as  a  prefix.) — One  million  times;  as  meg- 
ohm, one  million  ohms  ;  mega-volt,  one  million  volts. 
Hcidinger's  Voltaic  Cell.— (See  Cell,  Voltaic.) 
Meridian,  Geographic  —        —The  geopraphic  meri- 
dian of  a  place  is  a  great  circle  passing  through  the  place  and 
the  north  and  south  geographic  poles  of  the  earth. 


WORDS,  TERMS  AND  PHRASES.  415 

Meridian,  magnetic  —  —The  great  circle  passing 
through  the  poles  of  a  magnetic  needle  at  rest  in  the  earth's 
magnetic  field. 

Metallic  Arc. — A  voltaic  arc  formed  between  metallic 
electrodes.  (See  Arc,  Voltaic.) 

Metallic  Circuit.— Any  circuit  that  is  mainly  metallic 
throughout,  or  of  which  the  ground  or  earth  does  not  form  a 
part.  (See  Circuit,  Metallic.) 

Metallochromes  or  \ohiIiN  Ring*. — Prismatic 
colored  deposits  obtained  by  the  electrolytic  decomposition  of 
metallic  salts  under  certain  conditions. 

These  deposits  consists  of  peroxide  of  lead  which  appears 
at  the  positive  electrode.  The  colors,  like  those  produced  by 
soap-bubble  films,  or  by  the  iridescence  of  mother-of-pearl, 
or  by  films  of  oil  floating  on  the  surface  of  water,  etc.,  are 
due  to  the  interference  of  the  light  reflected  from  the  upper 
and  lower  surfaces  of  films  which  are  deposited  in  different 
thicknesses. 

Metalloid. — A  name  formerly  applied  to  a  non-metallic 
body,  or  to  a  body  having  only  some  of  the  properties  of  a 
metal  as  carbon,  boron,  oxygen,  etc. 

The  term  is  now  but  little  used. 

Metals,  Deflagration  of The  volatilization  of 

metals,  generally  by  electric  incandescence. 

Metals,  Electrical  Protection  of The  pro- 
tection of  a  metal  from  corrosion  by  placing  it  in  connection 
with  another  metal,  which,  when  exposed  to  the  corroding 
liquid,  vapor,  or  gas  will  form  with  the  metal  to  be  protected, 
the  positive  element  of  a  voltaic  couple. 

The  negative  element  of  a  voltaic  couple  is  protected  by  the 
presence  of  the  positive  element,  which  is  alone  corroded. 
This  method  has  been  adopted  with  considerable  success  to 


416  A  DICTIONARY  OF  ELECTRICAL 

electrically  protect  metals  from  corrosion.  A  few  examples 
will  suffice.  (See  Cell,  Voltaic.) 

(1)  Davy  proposed  to  protect  the  copper  sheathing  of  ships 
from  corrosion  by    attaching  pieces  of  zinc  to    the   copper 
sheathing.     This  succeeded  too  well  since  the  copper    salts 
which  were  formerly  produced  and  acted  as  a  poison  to  the 
marine  plants  and  animals,  being  now  absent,  permitted  these 
forms  of  life  to  thrive  to  such  an  extent  as  to  seriously  foul 
the  ship's  bottom. 

(2)  A  ring  of  zinc  attached  to  a  lightning  rod,  near  its  points 
has,  it  is  claimed,  the  power  of  protecting  the  points  from  cor- 
rosion. 

(3)  Iron  bars  of  railings,  if  sunk  or  embedded  in  zinc,  are  pre- 
served from  corrosion  near  the  junction  of  the  two  metals, 
but  if  sunk  in  lead  are  rapidly  corroded,  because  iron  is  elec- 
tro-positive to  lead,  but  electro-negative  to  zinc. 

(4)  Tinned  iron  rapidly  corrodes  or  rusts  when  the  iron  is  ex- 
posed to  the  atmosphere  by  a  scratch  or  abrasion,  because  the 
iron  is  electro-positive  to  tin.     Nickel-plated  iron,  for   the 
same  reason,  rusts  rapidly  on  the  exposure  of  an  abraded  sur- 
face. 

(5)  Zinced  or  galvanized  iron,  or  iron  covered  with  a  deposit 
of  zinc,  is  protected  from  corrosion  because  the  zinc,  being 
positive  to  iron,  can  alone  be  corroded,  and  the  zinc  is  pro- 
tected in  part  by  the  coating  of  insoluble  oxide  formed. 

Meter,  Current (See  Galvanometer.) 

Meter§,  Electric Apparatus  for  measuring 

commercially,  the  quantity  of  electricity  that  passes  in  a 
given  time,  through  any  consumption  circuit. 

Electric  meters  are  constructed  of  a  great  variety  of  forms  ; 
they  may,  however,  be  arranged  under  the  following  heads  : 

(1)  Electro-Magnetic  Meters,  or  those  in  which  the  current 
passing  is  measured  by  the  electro-magnetic  effects  it  pro- 
d.uces. 


WORDS,  TERMS  AND  PHRASES.  417 

In  such  meters  the  entire  current  may  pass  through  the 
meter. 

(2)  Electro- Chemical  Meters,  or  those  in  which  the  current 
passing  is  measured  by  the   electrolytic    decomposition    it 
effects. 

In  these  meters,  a  shunted  portion  only  of  the  current  is 
usually  passed  through  a  solution  of  a  metallic  salt,  and  the 
current  strength  determined  by  the  amount  of  electrolytic 
decomposition  thus  effected. 

(3)  Electro-Thermal  Meters,  or  those  in  which  the  current 
passing  is  measured  by  a  movement  effected  by  the  increase 
in  temperature  of  a  resistance  through  which  the  current 
is  passed,  or  by  the  amount  of  a  liquid  evaporated  by  the  heat 
generated  by  the  current. 

(4)  Electric-Time  Meters,  or  those  in  which  no  attempt  is 
made  to  measure  the  current  that  passes,  but  in  which  a 
record  is  kept  of  the  number  of  hours  that  an  electric  lamp, 
motor,  or  other  electro-receptive  device,  is  supplied  with  the 
current. 

Edison's  electric  meter  is  of  the  second  class.  It  consists  of 
two  voltameters,  or  electrolytic  cells,  containing  zinc  sulphate, 
in  which  two  plates  of  chemically  pure,  zinc  are  dipped.  The 
current  that  passes  is  determined  by  the  amount  of  the  varia- 
tion in  weight  of  the  zinc  plates.  To  determine  this,  the  plates 
are  weighed  at  stated  intervals  :  one  plate  every  month,  the 
other  plate,  which  is  intended  to  act  as  a  check  on  the  first,  only 
once  in  three  months.  Some  difficulty  has  been  experienced 
in  meters  of  this  class,  from  the  variations  in  the  value  of  the 
shunt  resistance,  due  to  variations  in  the  condition  and  tem- 
perature of  the  electrolytic  cell.  The  use  of  a  compensating 
resistance,  however,  has,  it  is  claimed,  removed  this  objec- 
tion. 

Methods  of  magnetization  »y  Touch.— 

These  are  three,  viz.: 

(1)  Single  Touch.     A  Method  for  effecting  the  magnetiza- 


418  A  DICTIONARY   OF  ELECTRICAL 

tion  of  a  bar  or  other  magnetizable  material  by  touch  from 
a  single  magnet. 

In  single  touch  the  magnetizing  magnet  is  simply  drawn 
over  the  bar  to  be  magnetized  from  end 


to  end  and  returned  through  the  air,  the 
stroke  being  repeated  a  number  of  times. 
The  end  of  the  pole  the  magnet  leaves 
is  thus  magnetized  oppositely  to  that  of 
the  magnetizing  pole. 

By  some  writers  the  method  of  single 

I+N  '      "s~]  touch  is  described  as  that  effected  by 

placing  the  magnetizing  magnet  N  S, 
Fig.  m.  Fig.  283,  on  the  middle  of  the  bar  to  be 

magnetized  and  drawing  it  to  the  end  and  returning  through 
the  air  as  before,  and  then  reversing  the  pole,  placing  it  on 
the  middle  of  the  bar,  and  drawing  it  towards  the  other  end. 
The  former  would,  however,  appear  to  be  the  better  use  of  the 
term  single  touch. 


Fig.  S8I,. 

(2)  Separate  Touch. 

In  separate  touch  two  magnetizing  bars  are  placed  with 
their  opposite  poles  at  the  middle  of  the  bar  to  be  magnetized 
and  drawn  away  from  each  other  towards  its  ends,  as  shown 


Fig.  S85. 

in  Fig.  284.     This  motion  is  repeated  a  number  of  times,  the 
poles  being  returned  through  the  air. 
In  the  above,  as  in  all  cases  of  magnetization  by  touch, 


WORDS,  TERMS  AND  PHRASES. 


419 


better  effects  are  produced  if  the  bar  to  be  magnetized  is  rested 
on  the  opposite  poles  of  another  magnet,  or  placed  near  them, 
as  shown  in  Fig.  285. 

(3)  Double  Touch. 

In  double  touch  the  two  magnets  are  placed  with  their 
opposite  poles  together  on  the  middle  of  the  bar  to  be  magnet- 
ized, as  shown  in  Fig.  285.  They  are  then  moved  to  one  end  of 
the  bar,  when,  instead  of  removing  them  and  passing  them 
back  through  the  air  to  the  other  end,  they  are  moved  in  this 
direction  over  the  bar  to  be  magnetized  to  the  other  end, 
and  this  motion  is  repeated  a  number  of  times.  The  motion  is 
stopped  at  the  middle  of  the  bar,  when  the  magnetizing  mag- 
nets are  moving  in  the 
opposite  direction  to 
that  at  which  they  be- 
gan to  move.  This 
assures  an  equal  num- 
ber of  strokes  to  the 
two  halves  of  the  bar. 
The  method  of  double 
touch  produces 
stronger  magnetiza-  Fig.  286. 

tion  than  either  of  the  other  methods  but  does  not  effect  such 
an  even  distribution  of  the  magnetism,  and  therefore  is  not 
applicable  to  the  magnetization  of  needles. 

A  variety  of  double  touch  is  shown  in  Fig.  286,  where  four 
bars  to  be  magnetized  are  placed  in  the  form  of  a  hollow 
rectangle,  with  only  their  ends  touching  at  their  edges,  the 
angular  spaces  at  the  corners  being  filled  with  pieces  of  soft 
iron.  The  horseshoe  magnet  N  S,  is  then  moved  around  the 
circuit  several  times  in  the  same  direction.  This  is  believed  to 
produce  a  more  uniform  magnetization  than  the  ordinary 
method  of  double  touch. 

Methven's  Standard  Screen.— An  upright  rectangular 
plate  of  metal,  furnished  with  a  vertical  slot  of  such  dimen- 


420  A  DICTIONARY  OF  ELECTRICAL 

sions  as  will  permit  an  Argand  burner,  the  flame  of  which  is 
three  inches  high,  to  send  through  the  slot  a  light  equal  to 
two  standard  candles. 

Metre  Bridge. — A  slide  form  of  Wheatstone's  electric 
balance,  in  which  the  slide  wire  is  one  metre  in  length.  (See 
Balance,  Wheatstone's  Slide  Form  of.) 

Metre  Candle.     (See  Candle,  Metre.) 

Metric  System  of  Weights  and  Measures.— A  sys- 
tem of  weights  and  measures  adopted  by  the  French,  and  by 
the  scientific  world  generally. 

For  measures  of  length,  the  one  ten-millionth  part  of  the 
quadrant  of  a  meridian  of  the  earth  is  taken  as  the  unit  of 
length.  This  unit  of  length  is  called  a  metr^,  and  various 
subdivisions  and  multiples  of  its  length  are  made  on  the 
decimal  system. 

For  a  system  of  weights,  the  weight  of  one  cubic  centimetre 
of  pure  water  at  39.2°  F.,  the  temperature  of  the  maximum 
density  of  water,  is  taken  as  the  unit  of  weight.  This  is  called 
a  gramme,  and  various  multiples,  and  subdivisions  of  this 
unit  are  made  on  the  decimal  system. 

The  following  table  of  French  measures  and  their  corres- 
ponding English  values  are  taken  from  Deschanel's  "  Element- 
ary Treatise  on  Natural  Philosophy  "  : 
Length. 

1  millimetre  =  .03937  inch,  or  about  ,V  inch. 

1  centimetre  =  .3937  inch. 

1  decimetre  =  3.937  inches. 

1  metre  =  39.3707  inches  =  3.281  ft.  =  1.0936  yd. 

1  kilometre  =  1093.6  yds.,  or  about  f  mile. 

More  accurately,  1  metre  =  39.370432  in.  =  3.2808693  ft.  = 
1.09362311  yd. 

Area. 

1  sq.  millimetre  =  .00155  sq.  inch. 


WORDS,  TERMS   AND  PHRASES.  421 

1  sq.  centimetre  =  .155  sq.  inch. 

1  sq.  decimetre  =  15.5  sq.  inches. 

1  sq.  metre  =  1550  sq.  inches  =  10.764  sq.  ft.  =  1.196  sq.  yd. 
Volume. 

1  cub.  millimetre  =  .OOOC61  cub.  inch. 

1  cub.  centimetre  =  .061025  cub.  inch. 

1  decimetre  =  61.0254  cub.  inches. 

Cubic  metre=  61025  cub.  in.  =  35.3156  cub.  ft.  =  1.308  cub.  yd. 

The  litre  (used  for  liquids)  is  the  same  as  the  cubic  deci- 
metre, and  is  equal  to  1.7617  pint,  or  .22021  gallon. 
Mass  and  Weight. 

1  milligramme  =  .01543  grain. 

1  gramme  =  15.432  grains. 

1  kilogramme  =  15432.3  grains  =  2.205  Ibs.  avoir. 

More  accurately,  the  kilogramme  is  2.20462125  Ibs. 
Miscellaneous. 

1  gramme  per  sq.  centimetre  =  2.0481  Ibs.  per  sq.  ft. 

1  kilogramme  per  sq.  centim.  =  14.223  Ibs.  per  sq.  in. 

1  kilogrammetre  =  7.2331  foot-pounds. 

1  force  de  cheval  =  75  kilogrammetres  per  second,  or  542^ 
foot-pounds  per  second,  nearly,  whereas  1  horse-power  (Eng- 
lish) =  550  foot-pounds  per  second. 

Conversion  of  English  into  French  measures  : 

Length. 

1  inch  =  2.54  centimetres,  nearly. 
1  foot  =  30.48  centimetres,  nearly. 
1  yard  =  91.44  centimetres,  nearly. 
1  statute  mile  =  160933  centimetres,  nearly. 
More  accurately,  1  inch  =  2.5399772  centimetres. 

Area. 

1  sq.  inch  =6.45  sq.  cm.,  nearly. 
1  sq.  foot  =  929  sq.  cm.,  nearly. 
1  sq.  yard  =  8361  sq.  cm.,  nearly. 
1  sq.  mile  =  2.59  x  1010  sq.  cm.,  nearly. 


422  A  DICTIONARY  OF  ELECTRICAL 

Volume. 

1  cub.  inch  =  16.39  cub.  cm.,  nearly. 
1  cub.  foot  =  28316  cub.  cm.,  nearly. 
1  cub.  yard  =  764535  cub.  cm. ,  nearly. 
1  gallon  =  4541  cub.  cm.,  nearly. 

Mass. 

1  grain  =  .0648  gramme,  nearly. 
1  oz.  avoir.  =  28.35  gramme,  nearly. 
1  Ib.  avoir.  =  453.6  gramme,  nearly.  > 
1  ton  =  1.016  x  106  gramme,  nearly. 
More  accurately,  1  Ib.  avoir.  =  453.59265  gm. 

Velocity. 

1  mile  per  hour  =  44.704  cm.  per  sec. 
1  kilometre  per  hour  =  27.7  cm.  per  sec. 

Density. 

1  Ib.  per  cub.  foot  =  .016019  gm.  per  cub.  cm. 
62.4  Ibs.  per  cub.  ft.  =  1  gm.  per  cub.  cm. 

Rorce  (assuming  g  =  981). 
Weight  of  1  grain  =  63.57  dynes,  nearly. 

"  1  oz.  avoir.  =  2.78  x  104  dynes,  nearly. 

"  1  Ib.  avoir.  =  4.45  x  105  dynes,  nearly. 

"  1  ton  =  9.97  x  10s  dynes,  nearly. 

"  1  gramme  =  981  dynes,  nearly. 

"  1  kilogramme  =  9.81  x  105  dynes,  nearly. 

Work  (assuming  g  =  981). 
1  foot-pound  =  1.356  x  107  ergs,  nearly. 
1  kilogrammetre  =  9.81  x  107  ergs,  nearly. 
Work  in  a  second  by  one  theoretical  "  horse  power"  =  7.46 
x  109  ergs,  nearly. 

Stress  (assuming  g  =  981). 

1  Ib.  per  sq.  ft.  =  479  dynes  per  sq.  cm.,  nearly. 
1  Ib.  per  sq.  inch  =  6.9  x  104  dynes  per  cm.,  nearly. 
1  kilog.  per  sq.  cm.  =  9.81  x  105  dynes  per  sq.  cm.,  nearly. 


WORDS,  TERMS  AND  PHRASES.  423 

760  mm.  of  mercury  at  0°  C.  =  1.014  x  106  dynes  per  sq.  cm., 
nearly. 

30  inches  of  mercury  at  0°  C.  =  1.163  X  106  dynes  per  sq. 
cm.,  nearly.  (DeschaneTs  Natural  Philosophy.) 

Mho. — A  term  proposed  by  Sir  Wm.  Thomson  for  the 
practical  unit  of  conductivity. 

A  mho  is  such  a  unit  of  conductivity  as  is  equal  to  the  re- 
ciprocal of  one  ohm. 

1 

The  conducting  power  is  equal  to  —  or  the  reciprocal  of  the 

R 
resistance. 

The  word  mho,  as  is  evident,  is  obtained  by  inverting  the 
order  of  sequence  of  the  letters  in  the  word  ohm. 

Micro  (as  a  prefix).— The  one  millionth  ;  as,  a  microfarad, 
the  millionth  of  a  farad  ;  a  microvolt,  the  one  millionth  of  a 
volt. 

Micrometer,  Arc An  apparatus  for  the  accurate 

measurement  of  the  length  of  a  voltaic  arc  by  means  of  a 
micrometer. 

The  distance  between  two  carbon  electrodes— one  mova- 
ble and  the  other  fixed — placed  inside  a  glass  vessel,  is  accu- 
rately determined  by  means  of  a  micrometer  placed  on  the 
movable  electrode.  The  operation  is  similar  to  that  of  the 
vernier  wire-gauge.  (See  Wire-Gauge,  Vernier.) 

Microphone.— An  apparatus  invented  by  Prof.  Hughes 
for  rendering  faint  or  distant  sounds  distinctly  audible. 

The  microphone  depends  for  its  operation  on  variations 
produced  in  the  resistance  of  the  circuit  of  a  small  battery  and 
receiving  telephone  by  means  of  a  loose  contact. 

The  loose  contact  may  take  a  variety  of  forms.  Originally, 
it  was  made  in  the  form  shown  in  Fig.  287,  in  which  a  small 
piece  of  carbon  E,  pointed  at  both  ends,  is  inserted  in  holes 
near  the  ends  of  cross  pieces  of  carbon  B  and  C.  The  thin 


424 


A  DICTIONARY  OF  ELECTRICAL 


upright  board  A,  on  which  these  are  supported,  acts  as  a 
sounding  board  or  diaphragm,  and  its  movements  by  sound 
waves  is  at  once  audible  to  a  person  listening  at  the  receiving- 
telephone.  The  walking  of  a  fly  over  the  sounding  board  is 
heard  as  a  very  much  louder  sound. 

The  forms  of  transmitting  telephone  invented  by  Reis, 
Edison.  Blake,  Berliner  and  others,  are  in  reality  varieties  of 
microphones. 


Fig.  287. 

microphone  Relay.— A  device  for  automatically  repeat- 
ing a  telephone  message  over  another  wire. 

A  form  of  microphone  relay  is  shown  in  Fig.  288. 

Several  minute  microphones,  mounted  on  the  diaphragm  of 
the  telephone  whose  message  is  to  be  repeated,  so  vary  the 
resistance  of  a  local  battery  included  in  their  circuit  as  to 
automatically  repeat  the  articulate  speech  received. 

The  microphones  may  be  connected  either  in  multiple-arc 
or  in  series,  as  shown  in  Fig.  289. 

Microtasimeter.— An  apparatus  invented  by  Edison  to 


WORDS,  TERMS  AND  PHRASES. 


425 


measure  minute  differences  of  temperature,  or  of  moisture,  by 
the  resulting  differences  of  pressure. 

A  change  of  temperature,  or  moisture,  is  caused  to  produce 
variations  in  the  resistance  of  a  button  of  compressed  lamp- 
black, placed  in  the  circuit  of  a  delicate  galvanometer.  The 


apparatus,  though  of  surprising  delicacy,  is  scarcely  capable 
of  practical  application,  from  the  fact  that  the  resistance  of 
the  carbon  docs  not  resume  its  normal  value  on  the  removal 
of  the  pressure.  t,«£  x 

Mil. — A  unit  of  length  used 
in  measuring  the  diameter  of 
wires,  equal  to  the  TTSVr  °f  an 
inch,  or  .001  inch. 


Mil,    Circular 


—A 


unit  of  area  employed  in  meas- 
uring the  areas  of  cross  sections  of  wires,  equal  to  .78540  square 
mil. 

One  circular  mil  =  .78540  square  mil. 

The  area  of  cross  section  of  a  circular  wire  one  mil  in  di- 
ameter is  equal  to  .78540  square  mil.    (See  Circular  Units,  etc.) 


426  A  DICTIONARY  Of  ELECTRICAL 

Mil,  Square A  unit  of  area  employed  in  measur- 
ing1 the  areas  of  cross  sections  of  wires,  equal  to  .000001  square 
inch. 

One  square  mil  =  1.2732  circular  mil. 

Milli  (as  a  prefix). — The  one-thousandth  part. 

Mill!- Ampere. — The  thousandth  of  an  ampdre. 

Milli-Oerstedt.— The  one-thousandth  of  an  Oerstedt 

mimosa  Sensitiva,  or  Sensitive  Plant.— A  sensitive 
plant  whose  leaves  fold  or  shut  up  when  touched. 

The  fibres  of  all  the  sensitive  plants,  such  for  example  as  the 
above,  the  Venus'  fly-trap,  ete.,  like  all  muscular  fibre,  and 
indeed  all  protoplasm,  suffer  contraction  when  traversed  by 
electric  currents. 

Pouillet  concludes  from  numerous  observations  that  the  free 
positive  electricity  of  the  atmosphere  is  partly  due  to  the  vapors 
disengaged  by  growing  plants. 

The  peculiar  geographical  distribution  of  thunder  storms, 
however,  does  not  favor  this  assumption. 

Mine  Exploder,  Electro-Magnetic (See  Ex- 
ploder, Electric.  Fuse,  Electric.) 

Miophone. — An  application,  by  Boudet,  of  the  micro- 
phone for  the  medical  examination  of  the  muscles. 

Mirror  Galvanometer.—  (See   Galvanometer,  Mirror.) 

Moisture,    Effect    of on     Electrical    Phe- 
nomena.— The  presence  of  moisture  on  the  surfaces  of  in- 
sulators permits  the  loss  or  dissipation  of  an  electric  charge. 
This  loss  is  more  rapid  with  negatively  charged  bodies  than 
with  those  positively  charged. 

Molar,  or  Mar§§  Attraction.— (See  Gravitation.) 
Molecular  Attraction. — (See  Attraction,  Molecular.) 
Molecular  Bombardment. — (See  Matter,  Radiant  or 
Ultra-Gaseous.) 


WORDS,  TERMS  AND  PHRASES.  427 

Molecular  Chain.— A  polarized  chain  of  molecules  that 
exists  in  an  electrolyte  during  its  electric  decomposition,  or  in 
a  voltaic  cell  on  closing  its  circuit.  (See  Grothuss1  Hypothesis.) 

molecular  Heat.— (See  Heat,  Molecular.) 

molecular  Rigidity,  or  Coercive  Force.— (See 
Coercive  Force.) 

Molecule,  Gramme The  weight  of  any  substance 

taken  in  grammes  numerically  equal  to  the  molecular  weight. 

The  gramme  molecule  represents  the  number  of  small  cal- 
ories of  heat  required  to  raise  one  gramme  of  the  substance 
through  1°  C.  (See  Calorie.) 

Moment  of  Couples. — (See  Couples,  Moment  of.) 

Moment,  Magnetic (See  Magnetic  Moment.) 

Monophotal  Arc  Light  Regulator.— A  term  some- 
times employed  to  distinguish  an  arc  electric  lamp  in  which 
the  whole  current  passes  through  the  arc  regulating  mechan- 
ism, and  which  is  usually  operated  singly  in  circuit  with  a 
dynamo.  Maier.  (See  Polyphotal.) 

Morse  Alphabet.— (See  Alphabet,  Morse.) 

Morse  Recorder,  or  Register.— (See  Recorder, 
Morse's.) 

Morse  System  of  Telegraphy.— (See  Telegraphy, 
Morse.) 

Morse's  Telegraphic  Sounder. — (See  Sounder, 
Morse's  Telegraphic.) 

Motograph,  Electro An  apparatus  for  the 

electric  transmission  of  signals,  in  which  the  receiving  instru- 
ment is  operated  by  the  slipping  of  a  lever  over  a  cylinder 
of  moistened  chalk,  on  the  passage  of  the  current.  (See  Elec- 
tro Motograph.) 

The  solution  for  moistening  the  paper  consists  of  sodium 
chloride  and  pyrogallic  acid  dissolved  in  water. 

Motor,  Electric  —  — A  device  for  transforming 

electric  power  into  mechanical  power. 


438  A  DICTIONARY  OF  ELECTRICAL, 

All  practical  electric  motors  depend  for  their  operation  on 
magnetic  attraction  or  repulsion.  The  entire  magnetism 
may  be  produced  by  the  current,  or  part  may  be  obtained 
from  permanent  magnets,  and  the  rest  from  electro  mag- 
nets. 

A  dynamo  electric  machine  will  act  as  a  motor  if  a  current 
is  sent  through  it.  Such  a  motor  is  sometimes  called  an 
electro  motor.  The  term  electric  motor  would,  however,  ap- 
pear to  be  the  preferable  one. 

In  all  cases  the  rotation  is  in  such  a  direction  as  to  induce  in 
the  armature  an  electromotive  force  opposed  to  that  of  the 
driving  current,  this  is  therefore  called  the  counter  electro- 
motive force. 

A  Magneto  Dynamo,  or  a  dynamo  the  field  of  which  is 
obtained  from  permanent  magnets,  or  a  Separately  Excited 
Dynamo,  will  operate  as  a  motor  when  a  current  is  sent 
through  its  armature,  and  will  turn  it  in  the  opposite  direction 
to  that  required  to  drive  it  in  order  to  produce  current. 

A  Series  Dynamo,  will  operate  as  a  motor  when  a  current  is 
sent  through  it.  If  the  current  is  sent  through  it  in  the  opposite 
direction  to  that  which  it  produces  when  in  operation  as  a  gener- 
ator, the  polarity  of  the  field  is  reversed  and  the  dynamo  will 
turn  as  a  motor  in  the  opposite  direction  to  that  required  to 
produce  the  current.  If  the  current  is  reversed  the  polarity 
of  both  the  field  and  the  armature  is  again  reversed,  and  the 
dynamo  still  rotates  as  a  motor  in  the  opposite  direction  to 
that  in  Avhich  it  is  rotated  as  a  generator. 

A  series  dynamo,  therefore,  always  rotates  as  a  motor  in  a 
direction  opposite  to  that  of  its  rotation  as  a  generator. 

When,  however,  the  polarity  of  the  field  only  is  reversed  by 
changing  the  connection  between  the  armature  and  the  field, 
the  rotation  is  in  the  same  direction. 

A  Shunt  Dynamo  operated  as  a  motor  will  also  turn  in  but 
one  direction,  but  this  direction  is  the  same  as  that  in  which 
it  turns  when  operating  as  a  generator;  for,  if  the  direction 


WORDS,  TERMS  AND   PHRASES.  429 

of  tne  current  in  the  armature  is  the  same  as  in  a  generator, 
that  in  the  shunt  is  revei'sed. 

A  Compound-Wound  Dynamo  will  move  in  a  direction 
opposite  to  that  of  its  motion  as  a  generator  if  the  series  part 
is  more  powerful  than  the  shunt,  and  in  the  same  direction  if 
the  shunt  part  is  more  powerful  than  the  series.  To  use  a 
compound-wound  dynamo  as  a  motor  it  is  necessary  merely 
to  reverse  the  connections  of  the  series  coils. 

Alternating- Current  Dynamo. — The  current  from  an  alter- 
nating-current dynamo,  if  sent  through  a  similar  alternating- 
current  dynamo  running  at  the  same  speed,  will  drive  it  as  a 
motor.  Such  a  machine  possesses  the  disadvantage  of  requir- 
ing to  be  maintained  at  a  speed  depending  on  that  of  the 
driving  dynamo,  and  also  that  it  requires  to  be  brought  to 
this  speed  before  the  driving  current  is  supplied  to  it.  .  As  a 
result  of  this  last  requirement,  variations  in  the  load  are  apt 
to  stop  the  motor.  Considerable  improvements,  however,  are 
being  introduced  into  alternate-current  motors,  by  which  these 
difficulties  are  almost  entirely  removed. 

An  alternating  current  sent  through  any  self -exciting 
dynamo-electric  machine,  such  as  a  shunt  or  series  machine, 
will  drive  it  continuously  as  a  motor.  The  sudden  reversals 
in  the  magnetization  of  its  cores  will,  however,  unless  they 
are  thoroughly  laminated,  set  up  powerful  eddy  currents  that 
will  injuriously  heat  the  machine. 

The  Reversibility  of  any  Dynamo-Electric  Machine,  or  its 
ability  to  operate  as  a  motor  if  supplied  with  a  current,  leads 
to  a  fact  of  great  importance  in  the  efficiency  of  electric 
motors.  This  fact  is  that  during  the  i-otation  of  the  armature 
there  is  induced  in  it,  during  its  passage  through  the  field  of 
the  machine,  an  electromotive  force  opposed  to  that  produced 
in  the  armature  by  the  driving  current,  or  a  counter-electro- 
motive force.  (See.  Spurious  Resistance.  Counter  Electro- 
motive  Force.}  This  counter  electro-motive  force  acts  as  a 
spurious  resistance,  and  opposes  the  passage  of  the  driving 


430  A  DICTIONARY  OF  ELECTRICAL 

current,  so  that,  as  the  speed  of  the  electric  motor  increases, 
the  strength  of  the  dl-iving  current  becomes  less,  until,  when 
a  certain  maximum  speed  is  reached,  no  current  passes.  In 
actual  practice,  this  maximum  speed  is  not  attained,  or  is 
only  momentarily  attained,  and  a  small,  nearly  constant,  cur- 
rent is  expended  in  overcoming  friction  at  the  bearings,  air 
friction,  etc. 

When,  however,  the  load  is  placed  on  the  motor,  that  is, 
when  it  is  caused  to  do  work,  the  speed  is  reduced  and  the 
counter  electromotive  force  is  decreased,  thus  permitting  a 
greater  current  to  pass.  The  fact  that  the  load  thus  auto- 
matically regulates  the  current  required  to  drive  the  motor, 
renders  electric  motors  very  economical  in  operation. 

The  relations,  between  the  power  required  to  drive  the 
generating  dynamo,  and  that  produced  by  the  electric  motor, 
are  such  that  the  maximum  work  per  second  is  done  by  the 
motor,  when  it  runs  at  such  a  rate  that  the  counter  electro- 
motive force  it  produces  is  half  that  of  the  current  supplied  to 
it.  The  maximum  work  or  activity  of  an  electric  motor  is 
therefore  done  when  its  theoretical  efficiency  is  only  50  per 
cent.  This,  however,  must  be  carefully  distinguished  from 
the  maximum  efficiency  of  an  electric  motor.  A  maximum 
efficiency  of  100  per  cent,  can  be  attained  theoretically,  and,  in 
actual  practice,  considerably  over  90  per  cent,  is  obtained.  In 
such  cases,  however,  the  motor  is  doing  work  at  less  than  its 
maximum  power. 

An  efficiency  of  100  per  cent,  is  reached  when  the  counter 
electromotive  force  of  the  motor  is  equal  to  that  of  the  source 
supplying  the  driving  current.  Supposing  now  the  driving 
machine  to  be  of  the  same  type  as  the  motor,  the  two 
machines  are  now  running  at  the  same  speed.  If  now  a  load 
is  put  on  the  motor  so  as  to  reduce  its  speed,  and  thus  permit 
it  to  produce  a  counter  electromotive  f o*'ce  of  but  90  per  cent. , 
its  efficiencj'  will  be  but  90  per  cent.  In  such  a  case,  therefore, 
the  efficiency  is  represented  by  the  relative  speeds  of  the  gener- 
ator and  the  motor. 


WORDS,  TERMS  AND  PHRASES.  431 

Motor  Electromotive  Force. — A  term  proposed  by 
F.  J.  Sprague  for  the  counter  electromotive  force  of  an  electric 
motor.  (See  Counter  Electromotive  Force.) 

This  term  was  proposed  by  Sprague  as  expressing  the 
necessity  for  the  existence  of  a  counter  electromotive  force  in 
an  electric  motor,  in  order  to  permit  it  to  utilize  the  energy 
of  the  electric  current  which  drives  it. 

"Motor.   Pyro-Magnetic (See    Pyro-Magnetic 

Motor.) 

Mouse-Mill. — A  form  of  convection  induction  machine 
invented  by  Sir  Wm.  Thomson  to  act  as  the  replenisher  of  his 
Electrometer.  (See  Electrostatic  Induction  Machines.  Re- 
plenisher.) 

Mouse-Mill  Dynamo,  sir  Win.  Thomson's 

A  dynamo  electric  machine  designed  by  Sir 

Wm.  Thomson,  named  from  the  resemblance  of  its  armature 
to  a  mouse  mill. 

The  armature  conductor  of  this  dynamo  consists  of  parallel 
bars  of  copper,  arranged  on  a  hollow  cylinder  like  the  bars  on 
a  mouse-mill. 

II  on  Hi  Pieces.— Openings  into  air-chambers,  generally 
circular  in  shape,  placed  over  the  diaphragms  of  telephones, 
phonographs,  gramophones,  or  graphophones  to  permit  the 
application  of  the  voice  in  speaking  so  as  to  set  the  diaphragm 
into  vibration. 

The  mouthpiece  may  also  be  utilized  by  the  ear  of  an 
observer  listening  so  as  to  be  affected  by  its  vibrations. 

Mover,  Prime In  a  system  of  distribution  of 

power  the  motor  by  which  the  others  or  secondary  movers  are 
driven. 

In  a  steam  plant  the  steam  engine  is  the  prime  mover;  the 
shafts  or  machines  driven  by  the  main  shafts  are  sometimes 
called  the  secondary  movers.  The  main  shaft  is  called  the 


432  A  DICTIONARY  OF  ELECTRICAL 

driving  shaft.     Its  motion  is  carried  by  means  of  belts  to 
other  shafts  called  driven  shafts.      The    belt    passes    over 
pulleys  on  the  driving  and  driven  shafts.    They  are  called  re- 
spectively the  driving  and  driven  putties. 
Multiple- Arc  Circuit.— (See  Circuits,  Varieties  of.) 
Multiple-Series,  Circuit.— (See  Circuits,  Varieties  of.) 
Multiple  Switch  Board.— (See  Board,  Multiple  Switch.) 

Multiplex  Telegraphy.— A  system  of  telegraphy  in 
which  more  than  four  messages  can  be  simultaneously  trans- 
mitted over  a  single  wire,  either  all  in  the  same  direction,  or 
part  in  one  direction,  and  the  remainder  in  the  opposite  direc- 
tion. (See  Telegraphy,  Multiplex.) 

Multiplier,  Schweigger's (See  Galvanometer.} 

Mutual  Induction. — (See  Induction,  Mutual.) 

Mn§cle§,  Electrical  Excitation  of (See   Elec- 

trotonus.) 

Muscular  Pile,  Matteucci's A  voltaic  battery  or 

pile,  the  elements  of  which  are  formed  of  longitudinal  and 
transverse  sections  of  muscle,  alternately  connected. 

Matteucci's  experiments  appear  to  show  that  the  lower  the 
animal  is  in  the  scale  of  creation,  the  stronger  is  the  current 
produced,  and  the  longer  its  duration.  Du  Bois-Reymond  has 
shown  that  the  muscular  current  is  not  due  to  contact,  but  to 
the  differences  of  electric  potential  naturally  possessed  by  the 
muscles  themselves. 

The  nerves  also  possess  the  power  of  producing  differences 
of  electromotive  forces  and  hence  currents.  (See  Electro- 
tonus.) 

Musket,  Electric A  gun  in  which  the  charge  is 

ignited  by  the  incandescence  of  a  platinum  wire  by  the  action 
of  a  battery  placed  in  the  body  of  the  gun. 

Myria  (as  a  prefix). — A  million  times. 


WORDS,  TERMS  AND  PHRASES.  433 

Nascent  State. — A  term  used  in  chemistry  to  express 
the  state  or  condition  of  an  elementary  atom  or  radical  just 
liberated  from  chemical  combination,  when  it  possesses  chem- 
ical affinities  or  attractions  more  energetic  than  afterwards. 

According  to  Grothuss'  hypothesis,  during  the  decomposi- 
tion of  a  chain  of  polarized  molecules,  such  for  example  as  that 
of  hydrogen  sulphate,  H3  SO4,  in  a  zinc-copper  voltaic  cell  the 
two  atoms  of  hydrogen  H2,  liberated  by  the  combination  of  the 
SO4,  with  an  atom  of  zinc  Zn,  possess  a  stronger  affinity  for  the 
SO4  of  the  molecule  next  to  it,  than  does  its  own  H2,  and  thus 
liberates  its  two  atoms  of  hydrogen,  which  in  turn  unite  with 
the  SO4,  of  the  next  molecule  in  the  polarized  chain,  and  this 
continues  until  the  two  atoms  of  hydrogen  liberated  from  the 
last  molecule  in  the  chain  are  given  off  at  the  surface  of  the 
copper  plate.  (See  Grothuss'  Hypothesis.) 

The  nascent  state  of  elements  is  doubtless  due  to  the  fact 
that  the  elements  are  then  in  a  free  state,  with  their  bonds 
open  or  unsatisfied,  and  therefore  possess  greater  affinities 
than  when  they  are  united  in  molecules.  Thus  H — ,  H — ,  or 
atomic  hydrogen,  should  possess  different  affinities  than  H  — H, 
or  molecular  hydrogen. 

Natural  Currents. — (See  Earth  Currents.) 

Natural  Law. — (See  Law,  Natural.) 

Natural  Hagiiet. — (See  Lodestone.   Natural  Magnet.) 

Needle,  A§tatie  —  —A  system  of  two  horizontal 

magnetic  needles,  with  the  opposite  poles  facing  each  other, 
rigidly  attached  to  a  vertical  support,  on  which  they  are  free 
to  turn.  (See  Astatic  Needle.) 

The  use  of  an  astatic  needle  lessens  the  force  required  to 
deflect  the  needle  either  in  the  earth's  field,  or  in  the  field 
of  another  magnet.  An  astatic  needle  is  shown  in  Fig.  290. 

Needle,  Dipping  —A  magnetic  needle,  sus- 
pended so  as  to  be  free  to  move  in  a  vertical  plane,  employed 
to  determine  the  deviation  of  the  needle  from  a  horizontal 


434  A  DICTIONARY  OF  ELECTRICAL 

position,  or  the  angle  of  dip,  or  magnetic  inclination  of  a 
place.  (See  Dip,  Magnetic.  Inclination,  Magnetic.  Incli- 
nometer. Inclination  Chart.) 

Needle,  Magnetic (See  Compass,  Azimuth.) 

Needle  of  Oscillation.— A  small  magnetic  needle  em- 
ployed for  measuring  the  intensity  of  a  magnetic  field  by 
counting  the  number  of  oscillations  the  needle  makes  in  a  given 
time,  when  disturbed  from  its  position  of  rest  in  such  field. 
(See  Intensity  of  Magnetization.  Isodynamic  Lines.) 

Needle,  Telegraphic A  needle  employed  in 

telegraphy,  the  movements  of  which  to  the  left  or  right 
respectively,  represent  the  dots  and  dashes  of  the  Morse 
alphabet.  (See  Telegraphy,  Needle  System.) 

Negative  Electricity.— One  of  the 

phases  or  states  of  electric  excitement. 
An  electrically  charged  body,  no 
matter  from  what  source  it  has  received 
its  charge,  manifests  either  a  negative 
or  a  positive  charge. 

According  to  the  Double  Fluid  Hy- 
pothesis, each  of  these  phases,  or 
varieties  of  electric  excitement,  is 
caused  by  the  presence  of  a  distinct 

and  separate    fluid,   endowed  with  characteristic  properties. 
According  to  the  Single  Fluid  Hypothesis,  negative  elec- 
tricity is  caused  by  the  deficit  of  a  single  fluid,  and  positive  elec- 
tricity by  a  surplusage  of  the  same  fluid. 

According  to  another  view,  negative  electricity  is  caused  by 
an  excess  of  the  universal  ether,  and  positive  electricity  by  its 
deficit.  (See  Hypotheses  of  Electricity.) 

Negative  Element  or  Plate,   of  a  Voltaic  Cell.— 

That  element  or  plate  of  a  voltaic  cell  into  which  the  current 
passes  from  the  exciting  liquid  of  the  cell. 


WORDS,  TERMS  AND  PHRASES. 


435 


The  plate  that  is  not  acted  on  by  the  electrolyte  during  the 
generation  of  current  by  the  cell.  The  copper,  or  carbon  plate 
respectively  in  a  zinc-copper,  or  zinc-carbon  couple. 

It  must  be  carefully  borne  in  mind  that  the  conductor  at- 
tached to  the  negative  element  of  a  voltaic  pile,  is  the  positive 
conductor  or  electrode  of  the  pile,  since  the  current  that  flows 
into  the  plate  from  the  liquid  or  electrolyte,  must  flow  out  of 
the  plate  where  it  projects  beyond  the  liquid. — (See  Cell,  Vol- 
taic, Polarity  of.) 

Serve  Fibre,  Electric  Excitability  of -(See 

Excitability,  Electric,  of  Nerve  Fibre.) 


Serves,  Action  of  Electricity  on 

trotonus.  Galvanization. 
Fardization.  Galvano- 
Faradization.) 


Set,  Faraday's 


Fig.  WL. 


— An  insulated  net  of  cot- 
ton gauze,  or  other  similar 
material,  capable  of  being 
turned  inside  out,  without 
being  thereby  discharged, 
employed  for  demonstrat- 
ing that  in  a  charged,  insu- 
lated conductor,  the  entire 
charge  is  accumulated  on  the  outside  of  the  conductor. 

Faraday's  net,  as  shown  in  Fig.  291,  consists  of  a  bag  N,  of 
cotton  gauze,  or  mosquito  netting,  supported  on  an  insulating 
stand  I.  When  tested  by  a  proof  plane,  no  free  electric  charge 
is  found  on  the  inside,  though  such  a  charge  is  readily  detected 
by  the  same  means  on  the  outside.  By  means  of  the  silk 
strings  S,  S,  the  bag  can  be  turned  inside  out,  when  the  charge 
will  then  all  be  found  on  the  then  inside  or  now  outside. 

Faraday  was  in  the  habit  of  protecting  his  delicate  electro- 
scopes against  outside  electrification  by  covering  them  with 


436  A  DICTIONARY   OF  ELECTRICAL 

gauze.  To  properly  act  as  an  electric  screen,  the  gauze  should 
be  connected  with  the  earth. 

Faraday  constructed  a  small  insulated  room,  twelve  feet  in 
height,  breadth,  and  depth,  covered  inside  with  tin-foil,  and. 
on  charging  this  room  from  the  outside,  he  was  unable  to  de- 
tect the  presence  of  the  charge,  even  by  the  aid  of  his  most 
delicate  instruments.  This  room  is  often  called  Faraday's 
Cube. 

Network  of  Currents— A  term  sometimrs  applied  to  a 
number  of  shunt  or  derived  circuits.  (See  Shunt  or  Derived 
Circuits.  Kirchoff's  Law.) 

Neutral  L,inc  of  Commutator  Cylinder.— (See  Line, 
Neutral,  of  Commutator  Cylinder.) 

Neutral  Point§  of  a  Dynamo  Eleetrie  Machine. 
— Two  points  of  greatest  difference  of  potential,  on  the  com- 
mutator cylinder,  situated  at  the  opposite  ends  of  a  diameter 
thereof,  at  which  the  collecting  brushes  must  rest  in  order  to 
carry  off  the  current  quietly. 

These  are  called  the  neutral  points  because  the  coils  that 
are  short  circuited  by  the  brushes  lie  in  the  magnetically  neu- 
tral points  of  the  armature.  (See  Line,  Neutral,  of  Commuta- 
tor Cylinder.) 

Neutral  Points  of  Thermo-Electric  Diagram.— 
The  points  on  a  thermo-electric  diagram  where  the  lines  rep- 
resenting the  thermo-electric  powers  of  any  two  metals  cross 
each  other. 

A  mean  temperature  for  any  two  metals  in  a  thermo-electric 
series,  at  which,  if  their  two  junctions  are  slightly  over  and 
slightly  under  the  mean  temperature  (the  one  as  much  above  as 
the  other  is  below),  no  differences  of  electromotive  force  are  de- 
veloped. (See  Diagram,  Thermo-Electric.  Couple,  Thermo- 
Electric.) 

Neutral  Points  on  a  Magnet.— Points  approximately 
midway  between  the  poles  of  a  magnet.  (See  Line,  Neutral, 
of  Magnet.  Equator  of  Magnet. ) 


WORDS,  TERMS  AND   PHRASES.  48? 

Nickel  Bath.— (See  Baths,  Nickel,  etc.) 

Non-Conductor*.  Insulators.— Substances  that  offer 
considerable  resistance  to  the  passage  of  an  electric  current 
through  their  mass. 

There  are  no  substances  known  that  absolutely  prevent  the 
flow  of  an  electric  current,  the  difference  of  potential  of  which 
is  sufficiently  great.  (See  Condtictors,  Table  of.} 

Notation,  Algebraic  — A  system  of  arbitrary 

symbols  employed  in  algebra. 

The  following  brief  description  of  the  notation  employed  in 
algebra  is  for  the  use  of  the  non-mathematical  reader: 

Quantities  are  represented  in  algebra  by  letters,  such  as  a 
and  b,  x,  and  y,  etc. 

Addition  is  represented  thus,  a  -\-  b. 

Subtraction  is  represented  thus,  a—  b. 

Multiplication  is  represented  thus,  axb,  or  simply  by  writ- 
ing the  letters  next  to  each  other  ab. 

a 

Division  is  represented  thus,  a  -=-  b,  or  —  . 

b 

An  Exponent,  or  figure  placed  to  the  right  of  a  letter,  above 
it  as  a8,  indicates  that  the  quantity  represented  by  a,  is  to 
be  multiplied  by  itself  three  times,  as  a  x  a  x  a,  or  a  a  a. 

A  Coefficient,  or  figure  placed  to  the  left  of  a  quantity,  in- 
dicates the  number  of  times  that  quantity  is  to  be  taken;  thus, 
3  a,  indicates  that  a  is  to  be  added  three  times,  thus  a  -f-  a  -j- 
a,  or  3  X  a. 

A  Radical  Sign  or  Root,  thus  |/  a,  or  2  \f'  a,  indicates  that  the 
square  root  of  the  quantity  a,  is  to  be  taken.  In  the  same 
manner  3 1/  a,  indicates  that  the  cube  root  of  a  is  be  taken. 

These  expressions  are  sometimes  written  a?,  or  a5. 
Equality  is  indicated  thus  :  a8  =  a  x  a  x  a,  or  a8 r  =  y'a. 


438  A  DICTIONARY   OP  ELECTRICAL 

1 

A  negative  exponent  er2  indicates  — ,  or  is  the  exponent  of 

a3 
the  reciprocal  of  the  quantity  indicated. 

IVuII  or  Zero  Methods.— Methods  employed  in  electrical 
measurements,  in  which  the  values  of  the  electromotive 
force  in  volts,  the  resistance  in  ohms,  or  the  current  in  amperes, 
or  other  similar  units,  are  determined  by  balancing  them 
against  equal  values  of  the  same  units,  and  ascertaining  such 
equality,  notb,y  the  deflections  of  the  needle  of  a  galvanometer, 
or  of  an  electrometer,  but  by  the  absence  of  such  deflections. 

The  advantage  of  zero-methods  is  found  in  the  fact  that  the 
galvanometer  or  electrometer  may  then  be  made  as  sensitive 
as  possible,  which  is  not  always  the  case,  since  great  deflec- 
tions are  generally  to  be  avoided,  especially  in  tangent  gal- 
vanometers.— (See  Galvanometers.  Electrometers.) 

Number,  Diaeritieal (See  Diacritical  Number.) 

Observatory,  magnetic An  observatory  in 

which  observations  of  the  variations  in  the  direction  and  in- 
tensity of  the  earth's  magnetic  field  are  made. 

Magnetic  observatories  are  generally  furnished  with  self- 
registering  magnetic  apparatus  such  as  magnetographs,  mag- 
netometers, inclinometers.  (See  Magnetometer.  Magneto- 
graph.  Inclinometer.) 

Magnetic  observatories  are  generally  constructed  entirely 
of  non-magnetic  materials,  that  is,  of  such  materials  as  are 
destitute  of  paramagnetic  properties. 

Occlusion  of  Oases.— The  absorption  or  shutting  up  of 
a  gas  in  the  pores,  or  on  the  surfaces  of  various  substances. 

Carbon  possesses  in  a  marked  degree  the  propei*ty  of  occlud- 
ing or  absorbing  gases  in  its  pores.  These  occluded  gases 
must  be  driven  out  from  the  carbon  conductor  employed  in 
an  incandescent  lamp,  since  otherwise  their  expulsion,  on 
the  incandescence  of  the  carbon  consequent  on  the  lighting 


WORDS,  TERMS  AND  PHRASES.  439 

of  the  lamp,  will  destroy  the  high  vacuum  of  the  lamp  cham- 
ber, and  thus  lead  to  the  ultimate  destruction  of  the  lamp. 
(See  Lamp,  Electric  Incandescent.) 

Odorscope. — An  apparatus  in  which  the  determination  of 
an  odor  was  attempted  by  the  measurement  of  the  effect  the 
odorous  vapor,  or  effluvia,  produced  on  a  variable  contact  re- 
sistance. 

The  microtasimeter  was  used  in  connection  with  the  odor- 
scope.  (See  Diagometer.  Microtasimeter.) 

Oerstedt,  An A  proposed  term  for  the  unit  of 

electric  current,  in  place  of  an  ampere. 

The  term  has  not  been  adopted. 

Ohm— The  unit  of  electric  resistance. 

Such  a  resistance  as  would  limit  the  flow  of  electricity  under 
an  electro-motive  force  of  one  volt  to  a  current  of  one  ampere, 
or  to  one  coulomb  per  second.  (See  B.A.  Unit.  Legal  Ohm. 
Standard  Ohm.) 

Ohm,  Legal (See  Legal  Ohm) 

Ohmic  or  True  Resistance.— The  true  resistance  of  a 
conductor  due  to  its  dimensions,  and  specific  conducting 
power,  as  distinguished  from  the  spurious  resistance  produced 
by  a  counter  electromotive  force.  (See  Counter  Electromo- 
tive Force.  Motors,  Electric.  Resistance,  Spurious.) 

Ohmmetcr. — A  commercial  galvanometer,  devised  by 
Ayrton,  for  directly  measuring  the  resistance  of  any  part  of  a 
circuit  through  which  a  strong  current  is  flowing,  by  the  de- 
flection of  a  magnetic  needle. 

Ayrton's  ohmmeter  is  represented  diagrammatically  in  Fig. 
292.  Two  coils  C  C,  and  c  c,  of  a  short  thick  wire,  and  of  a  long 
thin  wire,  respectively,  are  placed  at  right  angles  to  each  other, 
and  act  on  a  soft  iron  needle  situated  as  shown.  The  short 
thick  wire  coil  C  C,  is  connected  in  series  with  the  resistance 
O,  to  be  measured.  The  large  fine  wire  coil,  of  known  high 
resistance,  is  placed  as  a  shunt  to  the  unknown  resistance. 


440 


A  DICTIONARY   Of  ELECTRICAL 


Under  these  circumstances,  it  can  be  shown  that  the  action 
on  the  needle  is  due  to  the  ratio  of  the  difference  of  potential 
at  the  terminals  of  the  unknown  resistance,  and  the  current 

E 
strength  in  the  thick  wire  coil,  or,  R  —  — ,  as  may  be  deduced 

C 

from  Ohm's  law. 
The  coils  are  so  proportioned  that  the  current  when  flowing 


Fig.  SOS. 

through  the  short  thick  wire  moves  the  needle  to  the  zero  of 
the  scale,  while  the  long  thin  wire  produces  a  deflection 
directly  proportional  to  the  resistance. 


Ohm'§  L,aw.— The 


trength  of  the  current  in  any  circuit, 
is  directly  proportional  to 
the  difference  of  potential, 
or  electromotive  force  in 
that  circuit,  and  inversely 
C  proportional  to  the  resis- 
tance of  the  circuit,  i.  e.,  is 
equal  to  the  quotient  aris- 
ing from  dividing  the  elec- 


Fig.  293. 

tromotive  force  by  the  resistance. 
Ohm's  law  is  expressed  algebraically,  thus : 

E 

C  =  —  . 
R 


WORDS,  TERMS  AND  PHRASES.  441 

If  the  electro-motive  force  is  given  in  volts,  and  the  resis- 
tance in  ohms,  the  formula  will  give  the  current  strength 
directly  in  amperes. 

The  resistance  of  any  electric  circuit,  as  for  example  that 
shown  in  Fig.  293,  consists  of  three  parts,  viz.  : 

(1)  The  resistance  of  the  Source,  r. 

(2)  That  of  the  Conducting  Wires  or  Leads,  r',  and 

(3)  That  of  the  Electro-Receptive  Device,  r",  energized  by 
the  current.     Ohm's  law  applied  to  this  case  would  be 

E 


r+r'  +  r' 

That  is,  the  resistance  of  the  entire  series  circuit  is  equal  to 
the  sum  of  the  separate  resistances. 

T^  "R 

Since  C  =  —  ,  (1)  ;  then  E  =  C  R,  (3)  ;  and  R  =  —  ,  (3). 

R  C 

But,  since  a  current  of  one  ampere  is  equal  to  one  coulomb 
per  second,  then,  in  order  to  determine  in  coulombs  the  quan- 
tity of  electricity  passing  in  a  given  number  of  seconds,  it  is 
only  necessary  to  multiply  the  current  by  the  time  in  seconds, 
or  Q  =  C  T,  (4). 

Hence,  referring  to  the  above  equations  (1),  (2),  (3)  and  (4), 
according  to  Ohm's  law, 

(1)  The  current  in  amperes  is  equal  to  the  electromotive 
force  in  volts  divided  by  the  resistance  in  ohms. 

(2)  The  electromotive  force  in  volts  is  equal  to  the  product 
of  the  current  in  amperes,  and  the  resistance  in  ohms. 

(3)  The  resistance    in  ohms  is  equal  to   the  electromotive 
force  in  volts  divided  by  the  current  in  amperes. 

(4)  The  quantity  of  electricity  in  coulombs,  is  equal  to  the 
current  in  amperes  multiplied  by  the  time  in  seconds. 

Open  Circuit.—  (See  Circuit,  Broken.) 

Optical  Strain.—  A  deformation  or  alteration  of  volume 
produced  in  a  plate  of  glass,  or  other  transparent  medium,  by 
the  action  of  any  stress. 


442  A  DICTIONARY  OF  ELECTRICAL 

The  effect  of  this  strain  is  shown  by  the  action  of  the  medium 
on  abeam  of  plane  polarized  light. 

Optical  Strain,  Electro-magnetic A  strain 

produced  in  a  plate  of  glass  or  other  transparent  medium  by 
placing  it  in  a  magnetic  field.  (See  Electro- Magnetic  Stress. 
Magneto- Optic  Rotation.) 

Optical  strain,  whether  electrostatic  or  magnetic,  or  even  me- 
chanical, often  causes  a  medium  to  acquire  the  power  of  double 
refraction,  or  rotary  polarization.  (See  Double  Refraction, 
Electric.  Magneto  Optic  Rotation.) 

Optical  Strain,  Electrostatic A  strain  pro- 
duced in  a  plate  of  glass,  or  other  transparent  solid,  by  subject- 
ing it  to  the  stress  of  an  electrostatic  field.  ( See  Electrostatic 
Stress.) 

To  obtain  the  electrostatic  stress,  holes  are  drilled  in  the 
plate  of  glass,  and  wires  from  a  Holtz  machine  or  induction 
coil  placed  therein,  the  wires  being  separated  by  a  thin  layer  of 
glass.  The  glass,  on  being  traversed  by  a  beam  of  plane  po- 
larized light,  rotates  the  plane  of  its  polarization  in  the  same 
direction  as  the  glass  wouM  if  subjected  to  a  strain  in  the 
direction  of  the  lines  of  electric  force.  (See  Magneto-Optic 
Rotation.) 

Optic§,  Electro That  branch  of  electricity  which 

treats  of  the  general  relations  that  exist  between  light  and 
electricity. 

The  phenomena  of  electro-optics  may  be  arranged  under  the 
following  heads,  viz.: 

(1)  Electrostatic  Stress,  produced  by  an  electrostatic  field, 
causing  an  optical  strain  in  a  transparent  medium,  whereby 
such  medium  acquires  either  the  property  of  rotating  the 
plane  of  polarization  of  a  beam  of  plane  polarized  light,  or  of 
doubly  refracting  light. 

(2)  Electro-Magnetic  Stress,  produced  by  a  magnetic  field 
causing  an  optical  strain  in  a  transparent  medium,  whereby 
such  medium  acquires  either    the  property  of  rotating  the 


WORDS,  TERMS   AED  PHRASES.  443 

plane  of  polarization,  or  of  doubly  refracting  light.  (See  Po- 
larization of  Light.  Double  Refraction,  Electric.) 

(3)  Changes  in  the  electric  resistance  of  bodies  caused  by  the 
action  of  light.     (See  Selenium  Cell.) 

(4)  The  relation  existing  between  the  values  of  the  index 
of  refraction  of  a  transparent  medium  and  its  specific  induc- 
tive capacity.   (See  Refraction.   Specific  Inductive  Capacity.) 

This  relation  has  been  shown  to  be  as  follows  : 
The  specific  inductive  capacity  is  approximately  equal  to  the 
square  of  the  index  of  refraction. 

(5)  The  relation  existing  between  the  velocity  of  light  and 
the  value  of  the  ratio  of  the  electrostatic  and  the  electro-mag- 
netic units,  thus  giving  a  basis  for  an  electro-magnetic  theory 
of  light.    (See  Light,  Electro- Magnetic  Theory  of.) 

Ordinal*'*,  Axis  of (See  Abscissas,  Axis  of.) 

Ores,  Electric  Treatment  of (See  Furnaces, 

Electric.) 

Organ,  Electric A  wind  organ,  in  which  the 

escape  of  air  into  the  different  -pipes  is  electrically  con- 
trolled. 

In  an  electric  organ  the  keys,  instead  of  operating  levers 
as  usual  to  admit  the  passage  of  air  into  the  pipes,  merely 
make  the  circuit  of  a  battery  through  a  series  of  controlling 
electro-magnets.  With  such  an  arrangement,  the  keyboard 
can  be  placed  at  any  desired  distance. 

Electric  organs  have  been  constructed,  in  which  a  chemical 
or  mechanical  record  is  made  of  the  notes  struck  by  the  per- 
former, as  well  as  the  musical  value  of  these  notes.  By  such 
a  device  the  musical  creations  of  a  composer  are  permanently 
recorded  in  characters  that  are  capable  of  interpretation  by  a 
compositor  skilled  in  musical  notation. 

Oscillating  Discharge.— (See  Discharge,  Oscillating.) 
Oscillating  Needle.— (See  Needle  of  Oscillations.) 


444  A  DICTIONARY  OF  ELECTRICAL 

Oscillation,  Centre  of The  point,  in  a  body 

supported  so  as  to  swing  like  a  pendulum,  which  is  neither 
accelerated  nor  retarded  during  its  oscillations. 

The  centre  of  oscillation  is  always  below  the  centre  of  grav- 
ity. The  vertical  distance  between  the  centre  of  oscillation 
and  the  point  of  support  of  a  pendulum,  determines  the  virtual 
length  of  the  pendulum  and  hence,  its  number  of  vibrations 
per  second.  (See  Pendulum,  Laics  of.) 

Oscillations  Electric The  series  of  par- 
tial, intermittent  discharges,  of  which  the  apparent  instan- 
taneous discharge  of  a  Leyden  jar  through  a  small  resistance 
actually  consists. 

These  partial  discharges  produce  a  series  of  electric  oscilla- 
tions of  the  current  in  the  circuit  of  the  discharge,  which  con- 
sist of  a  true  to  and  fro,  or  backward  and  forward  motion  of 
the  electricity. 

Osmose. — The  unequal  mixing  of  liquids  of  different  dens- 
ities through  the  pores  of  a  separating  medium. 

If  a  solution  of  sugar  and  water  be  placed  in  a  bladder,  the 
neck  of  which  is  tied  to  a  straight  glass  tube,  and  the  bladder 
is  then  immersed  in  a  vessel  of  pure  water  with  the  tube  in  a 
vertical  position,  the  two  liquids  will  begin  to  mix,  the  sugar 
and  the  water  passing  through  the  bladder  into  the  pure  water, 
and  the  pure  water  passing  into  the  sugar  and  water  in  the 
bladder.  This  latter  current  is  the  stronger  of  the  two,  as  will 
be  shown  by  the  water  rising  in  the  vertical  glass  tube. 

The  stronger  of  the  two  currents  is  called  the  endosmotic 
current,  and  the  weaker  the  exosmotic  current. 

Osmose,  Electric A  difference  of  liquid  level 

produced  in  two  liquids  placed  on  opposite  sides  of  a  diaph- 
ragm on  the  passage  of  a  strong  electric  current  through  the 
liquids  between  two  electrodes  placed  therein. 

The  higher  level  is  on  the  side  towards  which  the  current 
flows  through  the  diaphragm,  thus  apparently  indicating  an 


WORDS,  TERMS  AND  PHRASES.  445 

onward  motion  of  the  liquid  with  the  current,  or  in  other 
words,  the  liquid  is  higher  about  the  kathode  than  the  anode. 
The  difference  of  level  is  the  more  marked  when  poorly  con- 
ducting liquids  are  employed. 

As  a  converse  of  this,  Quincke  has  shown  that  electric  cur- 
rents are  set  up  when  a  liquid  is  forced  by  pressure  through  a 
porous  diaphragm.  The  term  diaphragm  currents  has  been 
proposed  for  these  currents.  Their  electro-motive  force  de- 
pends on  the  nature  of  the  liquid,  on  the  material  of  the  dia- 
phragm, and  on  the  pressure  that  forces  the  liquid  through  the 
diaphragm.  (See  Electro- Capillary  Phenomena.) 

Output  of  Dynamo-Electric  Machines — The  elec- 
tric power  of  the  current  generated  by  a  dynamo-electric 
machine  expressed  in  volt-amperes,  or  watts. 

S.  P.  Thompson  suggests  that  dynamo-electric  machines  be 
rated  as  to  their  practical  safe  capacity  in  units  of  output  of 
1,000  watts,  or  one  kilo-watt.  According  to  this,  an  8-unit 
machine  might  give,  say  100  amperes  at  a  difference  of  poten- 
tial of  80  volts,  or  2,000  amperes  at  a  difference  of  potential  of 
four  volts.  Such  a  unit  would  be  far  more  expressive  than 
the  usual  method  of  rating  a  machine  as  having  a  capacity  of 
such  and  such  a  number  of  lights. 

Overtones. — Additional,  faint  tones,  accompanying  nearly 
every  distinct  musical  tone,  by  the  presence  of  which  its  pecu- 
liarity or  quality  is  produced.  (See  Quality,  or  Timbre.) 

Ozone. — A  peculiar  modification  of  oxygen  which  pos- 
sesses more  powerful  oxydizing  properties  than  ordinary 
oxygen. 

Ozone  is  now  generally  believed  to  be  tri-atomic  oxygen,  or 
oxygen  in  which  the  bonds  are  closed,  thus  : 
O 

A 

o — o 

The    peculiar  smell    observed    when  a  torrent  of    sparks 


446  A  DICTIONARY   OF  ELECTRICAL 

passes  between  the  terminals  of  a  Holtz  machine,  or  a  Ruhm- 
korff  coil,  is  caused  by  the  ozone  thus  formed. 

In  a  similar  manner  ozone  is  formed  in  the  atmos- 
phere during  the  passage  through  the  air  of  a  flash  of 
lightning. 

During  the  so-called  electrolysis  of  water,  some  of  the  oxy- 
gen is  given  off  in  the  form  of  ozone.  The  volume  of  the 
oxygen  liberated  is,  therefore,  somewhat  less  than  half  the 
volume  of  the  hydrogen. 

Palladium. — A  metal  of  the  platinum  group. 

Metallic  palladium  has  a  tin-white  color,  and,  when  polished, 
a  high  metallic  lustre.  It  is  tenacious  and  ductile,  and,  like 
iron,  can  be  welded  at  a  white  heat.  It  is  very  refractory  and 
possesses  in  a  marked  degree  the  power  of  absorbing  or 
occluding  hydrogen  and  other  gases.  It  is  not  affected  by 
oxygen  at  any  temperature,  nor  readily  affected  by  ordinary 
corrosive  agents. 

Palladium  Alloys.— Alloys  of  palladium  with  other 
metals. 

Palladium  forms  a  number  of  useful  alloys  with  various 
metals.  Some  of  the  alloys  are  as  elastic  as  steel,  are  un- 
affected by  moisture  or  ordinary  corrosive  agencies,  and  are 
entirely  devoid  of  paramagnetic  properties. 

These  properties  have  been  utilized  by  their  discoverer, 
Paillard,  in  their  employment  for  the  hair-springs,  escape- 
ments and  balance  wheels  of  watches,  in  order  to  permit  the 
watches  to  be  carried  into  strong  magnetic  fields  without  any 
appreciable  effects  on  the  rate  of  the  watch.  A  number  of 
careful  tests  made  by  the  author,  by  long  continued  ex- 
posure of  watches,  thus  protected  by  the  Paillard  alloys, 
in  extraordinary  iields,  show  that  the  protection  thus 
given  the  watches  enables  them  to  be  carried  into  the 
strongest  possible  magnetic  fields  without  appreciably  affect- 
ing their  rate. 


WORDS,  TERMS  AND   PHRASES.  447 

The  Paillard  palladium  alloys  have  the  following  composi- 
tion, viz.: 

Alloy  No.  1. 

Palladium 60  to  75  parts. 

Copper 15  to  25       " 

Iron 1  to    5       " 

Alloy  No.  2. 

Palladium 50  to  75       " 

Copper .20  to  30       " 

Iron 5  to  20      " 

Alloy  No.  3. 

Palladium .65  to  75      " 

Copper.. 15  to  25       " 

Nickel. Ito    5       " 

Gold..     Ito    2^" 

Platinum %  to    2       " 

Silver 3  to  10       " 

Steel. Ito    5       " 

Alloy  No.  4. 

Palladium 45  to  50      " 

Silver 20  to  25       •' 

Copper 15  to  25       " 

Gold.. 2to    5       " 

Platinum 2  to    5       " 

Nickel 2to    5      " 

Steel 2to    5      " 

The  great  value  of  these  alloys,  when  employed  for  the  hair- 
springs of  watches,  arises  not  only  from  their  non-magnetiz- 
able properties,  and,  their  inoxidizability,  but  particularly 
from  the  fact  that  their  elasticity  is  approximately  the  same 
for  comparatively  wide  ranges  of  temperature. 

Pane,  IWagic  —        —  A  sheet  of  glass  covered  with  pieces 
of  tin  foil  with  small  spaces  between  them  pasted  in  some  de- 
sign on  the  glass. 
On  the  discharge  of  a  Leyden  jar  through  these  metallic 


448  A  DICTIONARY  OF  ELECTRICAL 

pieces,  the  design  is  seen  as  a  series  of  minute  sparks  that 
bridge  the  spaces  between  the  adjacent  pieces  of  foil. 

Paiitelejf  raplij ,     or    Facsimile    Telegraphy.— A 

system  for  the  telegraphic  transmission  of  charts,  diagrams, 
sketches  or  written  characters.  (See  Telegraphy,  Facsi- 
mile.) 

Paper  Carbons. — Carbon,  of  textile  or  fibrous  origin, 
obtained  from  the  carbonization  of  paper. 

The  carbonization  of  paper  is  readily  effected  by  submitting 
it  to  the  prolonged  action  of  a  high  temperature  while  out  of 
contact  with  air. 

For  this  purpose  the  paper  is  packed  in  retorts  or  crucibles, 
and  covered  with  lamp-black,  or  powdered  plumbago,  in 
order  to  exclude  the  air. 

Since  paper  consists  of  a  plane  of  material  uniformly  thin 
in  one  direction,  formed  almost  entirely  of  fibres  6f  pure  cel- 
lulose, the  greatest  length  of  which  extend  in  a  direction 
nearly  parallel  to  that  in  which  the  paper  is  uniformly  thin, 
it  is  clear  that  sheets  of  this  substance,  when  carbonized, 
should  yield  flexible  carbons  of  unusual  purity  and  electrical 
homogeneity,  since  such  carbons  are  structural  in  character, 
and  are  uniformly  affected  by  the  heat  of  carbonization,  to  an 
extent  that  would  be  impossible  by  the  carbonization  of  any 
material  in  a  mass. 

Paper  Perforator.— An  apparatus  employed  in  systems 
of  automatic  telegraphy  for  punching  in  a  fillet  of  paper, 
circular  or  elongated  spaces  that  produce  the  dots  and  dashes 
of  the  Morse  alphabet,  when  the  fillet  is  drawn  between  metal 
terminals  that  form  the  electrodes  of  a  battery.  (See  Teleg- 
raphy, Automatic.) 

Parabolic  Reflector.— A  reflector,  or  mirror,  the  reflect- 
ing surface  of  which  is  a  paraboloid,  or  such  a  surface  as 
would  be  obtained  by  the  revolution  of  a  parabola  about  its 
axis, 


WORDS,  TERMS  AND  PHRASES.  449 

A  parabolic  curve,  which  may  be  regarded  as  a  section  of  a 
parabola,  is  shown  in  Fig.  294.  A  parabola  has  the  following 
properties  :  If  lines  F  P,  F  P,  etc.,  be  drawn  from  the  point 
F,  called  the  focus,  to  any  point,  P,  P,  etc.,  in  the  curve,  and 
the  lines  Pp,  Pp,  Pp,  etc.,  be  then  drawn  severally  parallel  to 
the  axis,  V  M,  then  all  such  angles,  F  Pp,  F  Pp,  will  be 
bisected  by  verticals  to  tangents  at  the  point  P,  P,  and  P. 

Therefore,  if  a  light  be  placed  at  the  focus  of  a  parabolic 
reflector,  all  the  light  reflected  will  pass  off  sensibly  parallel 
to  the  axis  V  M. 

In  locomotive  head  lights,  a  lamp  is  placed  at  the  focus  of  a 
parabolic  reflector,  and  the  parallel  beam  so  obtained  utilized 
for  the  illumination  of  the  track.  In  a  search 
light,  an  electric  arc  lamp  is  placed  in  a  para- 
bolic reflector,  or  at  the  focus  of  a  lens. 

A  parabolic  reflector,  such  as  is  used  for 
search  lights,  is  shown  in  Fig.  295.  A  fo- 
cussing arc  lamp  must  be  used  for  this  pur- 
pose,  so  as  to  maintain  the  voltaic  arc  at ' 
the  focus  of  the  parabolic  reflector,  notwith- 
standing the  consumption  of  the  carbons. 

Parafflnc. — The  name  given  to  various 
solid  hydrocarbons,  of  the  marsh-gas  series,          Fig.  204. 
that  are  derived  from  coal  oil  or  petroleum  by  the  action  of 
nitric  acid. 

Parafine  possesses  excellent  powers  of  insulation,  and  forms 
a  good  dielectric  medium.  Dried  wood,  boiled  in  melted  par- 
affine,  forms  a  fair  insulating  material. 

Paragreles. — Lightning  rods,  intended  to  protect  fields 
against  the  destructive  action  of  hail.  (See  Hail,  Assumed 
Electrical  Origin  of.) 

It  was  formerly  believed  that  hail  is  caused  by  electricity. 
It  is  now  generally  believed  that  the  electricity  in  hail  storms 
is  caused  by  the  hail.  It  will  therefore  readily  be  understood 
that  paragr^les  can  afford  no  real  protection. 


450 


A  DICTIONARY  OF  ELECTRICAL 


Parallax. — The  apparent  angular  displacement  of  an  ob- 
ject when  seen  from  two  different  points  of  view. 

In  reading  the  exact  division  on  a  scale  to  which  a  needle 
points,  care  must  be  taken  to  look  directly  down  on  the  needle, 
and  not  sideways,  so  as  to 
avoid  the  error  of   displace- 
ment due  to  parallax. 

Parallel  Circuit.— A 
name  sometimes  applied  to 
circuits  connected  in  multiple- 
arc.  (See  Circuits,  Varieties 
of.) 

Parallelogram  of 
Force§.— (See  Forces,  Par- 
allelogram of.) 

Paramagnetic.  —  Sub- 
stances  possessing  the  proper- 
ties ordinarily  recognized  as 
magnetic. 

Substances  possessing  the 
power  of  concentrating  the 
lines  of  magnetic  force  on 
them. 

Paramagnetic  is  a  term  em- 
ployed in  centra-distinction 
to  diamagnetic.  (See  Dia- 
magnetic.)  A  paramagnetic 
substance,  cut  in  the  form 
of  a  bar  whose  length  is  much  greater  than  its  breadth  and 
thickness,  when  suspended  in  a  magnetic  field  in  the  manner 
shown  in  Fig.  296,  will  take  up  a  position  of  rest  with  its 
greatest  length  in  the  direction  of  the  lines  of  force,  i.  e., 
will  point  axially.  In  other  words  the  lines  of  force  will  so 
pass  through  the  paramagnetic  substance  as  to  reduce  the 
magnetic  resistance  of  the  circuit  as  much  as  possible. 


Fig.  295. 


WORDS,  TERMS  AND  PHRASES. 


451 


Paramagnetic  substances,  therefore,  concentrate  the  lines  of 
force  on  them.  (See  Resistance,  Magnetic.) 

Diamagnetic  substances,  on  the  contrary,  placed  as  shown 
in  Fig.  296,  assume  a  position  of  rest  with  their  least  dimen- 
sions in  the  direction  of  the  lines  of  force,  i.  e.,  they  point 
equatorially.  This  is  the  position  in  which  they  are  placed  by 
the  lines  of  force,  in  order  to  ensure  the  least  magnetic  resist- 
ance in  the  circuit  of  these  lines.  The  magnetic  resistance  of 
diamagnetic  substances  is  great  as  compared  with  that  of 
paramagnetic  substances. 

The  term  ferro-magnetic  has  been  proposed  for  paramag- 
netic. If  another  term  be  required,  which 
is  doubtful,  sidero-magnetic  proposed  by 
S.  P.  Thompson,  would  be  far  prefer- 
able. (See  Ferro-Magnetic.  Sidero-Mag- 
netic.) 

Tyndall  believes  that  the  magnetic  po- 
larity possessed  by  diamagnetic  substances 
is  a  distinct  polar  force,  different  in  its 
nature  from  ordinary  magnetiism.  (See 
Polarity,  Diamagnetic.) 

Parainagnetism.  —  The  magnetism 
of  a  paramagnetic  substance. 

Parasitical  Currents — (See  Cur- 
rents, Eddy,  Foucault,  or  Local.) 

Paratonncrcs. — A  French  term  for 
lightning  rods,  sometimes    employed    in    English    technical 
works. 

Lightning  rod  would  appear  to  be  the  preferable  term. 

Partial  Earth.    (See  Earths.) 

Passive  State.— The  condition  of  a  metallic  substance 
in  which  it  may  be  placed  in  liquids  that  would  ordinarily 


Fig.  206. 


452  A  DICTIONARY   OF  ELECTRICAL 

chemically  combine  with  it,  without  being  attacked  or  cor- 
roded. 

It  is  very  doubtful  whether  metallic  bodies  can  be  properly 
regarded  as  possessing  an  actual  passive  state.  Iron,  for 
example,  which  is  one  of  the  metals  that  is  said  to  be  capa- 
ble of  assuming  this  so  called  passive  state,  can  be  placed 
in  this  condition  by  immersing  it  for  a  few  moments  in  concen- 
trated nitric  acid,  and  subsequently  washing  it.  It  will  then, 
unlike  ordinary  iron,  neither  be  attacked  by  concentrated 
nitric  acid,  nor  will  it  precipitate  copper  from  its  solutions. 
This  condition  is  now  generally  believed  to  be  due  to  the  for- 
mation of  a  thin  coating  of  magnetic  oxide  on  its  surface. 

Many  of  the  instances  of  the  so-called  passive  state  are 
simply  cases  of  the  well  known  electrical  preservation  of 
metals  that  form  the  negative  element  of  a  voltaic  combina- 
tion, under  which  circumstances  the  positive  element  only  of 
the  voltaic  couple  is  chemically  attacked  by  the  electrolyte. 
(See  Cell,  Voltaic.  Metals,  Electrical  Preservation  of .) 

P.  D.  or  p.  d. — A  contraction  frequently  employed  for 
difference  of  potential.  (See  Difference  of  Potential.) 

Peltier  Effect.— (See  Effect,  Peltier.) 

Pendulum,  Electric A  pendulum  so  arranged 

that,  in  its  to-and-fro  motions,  it  sends  electric  impulses  over 
a  line,  either  by  making  and  breaking  contacts,  or  such  in 
which  the  to  and  fro  movements  are  maintained  by  electric 
impulses. 

Such  pendulums  are  employed  in  systems  for  the  electrical 
distribution  of  time. 

Sometimes,  instead  of  using  true  pendulums  for  such  pur- 
poses, coils,  or  contact  points,  mounted  on  the  ends  of  flexible 
bars  of  steel  called  reeds,  or  on  tuning  forks,  are  often  used 
for  the  purpose  of  establishing  currents,  or  modifying  the  cur- 
rents that  are  already  passing  in  a  circuit.  The  movement 
of  a  magnetic  diaphragm,  as  in  the  case  of  a  telephone 


WORDS.  TERMS  AND  PHRASES.  453 

diaphragm,  towards  and  from  a  coil  of  wire  is  another  illustra- 
tion of  an  electric  pendulum. 

Pendulum,  Law*  of—  —The  laws  which  ex- 

press the  peculiarities  of  the  motion  of  a  simple  pendulum. 

A  simple  pendulum  is  one  in  which  the  entire  weight  is  con- 
sidered as  concentrated  at  a  single  point,  suspended  at  the 
end  of  a  weightless,  inflexible,  and  inextensible  line. 

The  following  are  the  laws  of  the  simple  pendulum  : 

(1)  Oscillations    of    small    amplitude     are    approximately 
isochronous;  that  is,   are  made  in  times  that  are  sensibly 
equal.     (See  Amplitude  of  Vibration.     Isochronism.) 

(2)  In  pendulums  of  different  lengths,   the 
duration  of  the  oscillations  is  proportional  to 
the  square  root  of  the  length  of  the  pendulum. 

(3)  In  the  same  pendulum,  the  length  being 
preserved    invariable,     the    duration    of    the 
oscillation  is    inversely    proportional    to    the 
square  root  of  the  intensity  of  gravity. 

The  intensity  of  gravity  at  any  latitude,  may 
be  determined  by  the  number  of  oscillations  of  fiff  •  ^9 
a  pendulum  of  a  given  length.  In  the  same  manner  iheinten- 
sity  of  a  magnetic  field,  or  the  intensity  of  'magnetization  of 
a  magnet,  may  be  determined  by  the  needle  of  oscillation, 
by  observing  the  number  of  oscillations  a  needle  makes  in 
a  given  time  when  disturbed  from  its  position  of  rest.  (See 
Needle  of  Oscillation.} 

Since  a  simple  physical  pendulum  is  a  physical  impossibility, 
the  virtual  length  of  a  pendulum,  that  is,  the  vertical  distance 
between  its  point  of  support  to  the  centre  of  oscillation  is 
taken  as  the  true  length  of  the  pendulum. 

If  the  irregularly  shaped  body,  shown  in  Fig.  297,  whose  cen- 
tre of  gravity  is  at  G,  is  made  to  swing  like  a  pendulum,  either 
on  S,  or  O,  its  oscillations  will  be  performed  in  equal  times,  and 


454  A  DICTIONARY  OF  ELECTRICAL 

the  body  will  act  as  a  simple  pendulum,  whose  virtual  length 
is  SO. 

If,  while  suspended  at  S,  it  be  struck  at  O,  it  will  oscillate 
around  S,  witbout  producing  any  pressure  on  the  supporting 
axis  at  S,  on  which  it  turns.  If  floating  entirely  submerged 
in  a  liquid,  a  blow  at  O  would  cause  it  to  move  in  a  straight 
line,  in  the  direction  of  the  blow,  without  rotation. 

The  point  O,  is  called  the  centre  of  percussion,  or  the  centre 
of  oscillation.  The  centre  of  oscillation  is  always  below  the 
centre  of  gravity. 

Pen,  Electric A  device  for  manifold  copying,  in 

which  a  sheet  of  paper  is  made  into  a  stencil  by  minute  per- 
forations obtained  by  a  needle  driven  by  a  small  electric  motor. 
The  stencil  is  afterwards  employed  in  connection  with  an  inked 
roller  for  the  production  of  any  required  number  of  copies. 

Mechanical  pens  are  constructed  on  the  same  principle,  the 
perforations  being  obtained  by  mechanical  instead  of  by 
electric  power. 

Percussion,  Centre  of That  point  in  a  body, 

suspended  so  as  to  move  as  a  pendulum  at  which  a  blow 
would  produce  rotation,  but  no  forward  motion,  or  motion 
of  translation. 

Periodicity  ol  Auroras  and  magnetic  Storms.— 

Observed  coincidences  between  the  occurrence  of  auroras  and 
magnetic  storms,  and  sun  spots. 

The  periodical  occurrence  of  auroras,  or  magnetic  storms, 
both  as  to  frequency  and  intensity,  which,  occuring  at  periods 
of  about  eleven  years  apart,  corresponds  to  the  well-know 
eleven-year  sun-spot  period. 

It  also  agrees  with  a  variation  in  the  magnetic  declination  of 
a  place  which,  according  to  Sabine,  occurs  once  in  every 
eleven  years. 

Permanent  Ifla^net. — (See  Magnet,  Permanent.) 


WORDS,  TERMS  AND  PHRASfiS.  455 

Permanent  State  of  Charge  of  Telegraph  Line* 

— (See  State,  Permanent.} 

Permeability,  Magnetic The  ease  afforded 

by  any  substance  to  the  passage  through  it  of  lines  of  mag- 
netic force. 

The  magnetic  permeability  of  paramagnetic  substances  is 
much  less  than  that  of  diamagnetic  substances.  A  substance 
of  great  magnetic  permeability  has  small  magnetic  resistance, 
or  possesses  small  magnetic  reluctance  to  magnetization.  (See 
Paramagnetic.  Diamagnetic.  Magnetic  Reluctance.) 


fig.  S98. 

Phenomena,  Electro  Capillary (See  Elec- 
tro-Capillary Phenomena.) 
Pherope  or  Telephote.— (See  Telephote.) 

Phial,  L,eyden (See  Jar,  Ley  den.) 

Philosopher's  Egg. — (See  Discharge,  Convective.) 
Phonautograph.— An  apparatus  for  the  automatic  pro- 
duction of  a  visible  tracing  of  the  vibrations  produced  by  any 
sound. 


456 


A  DICTIONARY   OF   ELECTRICAL 


Phonautographic  apparatus  consists  essentially  of  devices 
by  which  the  sound  waves  are  caused  to  impart  their  to-and- 
fro  movements  to  a  diaphragm  at  the  centre  of  which  a  pencil 
or  tracing  point  is  attached.  The  record  is  received  on  a  sheet 
of  paper,  or  wax,  or  on  a  smoked  glass  or  other  suitable  sur- 
face. 

Leon  Scott's  Phonautograph,  which  is  among  the  forms 
best  known,  consists  of  a  hollow  conical  vessel  A,  Fig.  298,  with 
a  diaphragm  of  parchment  stretched  tightly  like  a  drum-head 
over  its  smaller  aperture  B.  A  tracing  point,  attached  to  the 


JIT 


Fig. 


centre  of  the  diaphragm,  traces  a  sinuous  line  on  the  surface 
of  a  soot-covered  cylinder  C,  that  is  uniformly  rotated  under 
the  tracing  point.  As  the  cylinder  is  advanced  a  short  dis- 
tance with  every  rotation,  a  sinuous  spiral  line  is  traced  on  the 
surface. 

Phonic  Wheel.— A  wheel  to  which  is  attached  a  circular 
table  of  contact  points,  that  is  maintained  in  synchronous 
rotation  by  means  of  a  timed  series  of  electric  impulses  sent 
over  a  line. 


WOEDS,  TERMS  AND  PHRASES.  457 

The  phonic  wheel  was  invented  by  La  Cour,  but  was  first 
put  into  successful  operation  in  multiplex  telegraphy  by 
Delany  in  his  system  of  Synchronous  Multiplex  Telegraphy. 
(See  Telegraphy,  Synchronous,  Multiplex.)  Delany  obtains 
the  exact  synchronism  of  the  phonic  wheel  by  a  series  of  cor- 
recting- electric  impulses,  automatically  sent  over  the  line  on 
the  failure  of  the  phonic  wheel  at  either  end  of  the  line  to 
exactly  synchronise  with  that  at  the  other. 

Phonograph.— An  apparatus  for  the  reproduction  of 
articulate  speech,  or  of  sounds  of  any  character,  at  any  in- 
definite time  after  their  occurrence  and  for  any  number  of 
times. 

In  Edison's  phonograph  the  voice  of  the  speaker,  received 
by  an  elastic  diaphragm  of  thin  sheet  iron,  or  other  similar 
material,  is  caused  to  indent  a  sheet  of  tin-foil  placed  on  the 
surface  of  a  cylinder  C,  Fig.  299,  that  is  maintained  at  a  uni- 
form rate  of  rotation  by  the  crank  at  W.  In  the  form  shown, 
the  motion  is  by  hand,  In  a  later  improved  form  the  cylinder 
is  driven  by  means  of  an  electric  motor,  or  by  clockwork. 

In  order  to  reproduce  the  speech  or  other  sounds  the  phono- 
gram record  is  placed  on  the  surface  of  a  cylinder  similar  to 
that  on  which  it  was  received,  (or  is  kept  on  the  same  surface), 
and  the  tracing  point,  placed  at  the  beginning  of  the  record 
and  being  maintained  against  it  by  gentle  pressure,  is  caused,  by 
the  rotation  of  cylinder,  to  follow  the  indentations  of  the  pho- 
nogram record.  As  the  point  is  thus  moved  up  and  down  the 
hills  and  hollows  of  the  record  surface,  the  diaphragm  to  which 
it  is  attached  is  given  a  torand-fro  motion  that  exactly  corres- 
ponds to  the  to-and-fro  motion  it  had  when  impressed 
originally  by  the  sounds  it  has  recorded  on  the  phonogram 
record.  A  pel-son  listening  at  this  diaphragm  will  therefore 
hear  an  exact  reproduction  of  the  sounds  originally  uttered. 

In  this  manner,  the  voices  of  relatives,  distinguished  sing- 
ers, or  statesmen  can  be  preserved  for  future  generations. 


458 


A  DICTIONARY  Of  ELECTRICAL 


In  Edison's  improved  phonograph,  the  record  sunface  con- 
sists of  a  cylinder  of  hardened  \vax.  The  motion  of  the  cylin- 
der is  obtained  by  means  of  an  electric  motor.  Two  diaphragms 
are  used,  one  for  recording,  and  one  for  reproducing.  As 
shown  in  Fig.  300,  the  recording  diaphragm  is  in  position 
against  the  cylinder.  The  recording  diaphragm  is  made  of 
malleable  glass.  The  reproducing  diaphragm  is  formed  of 
bolting  silk  covered  with  a  thin  layer  of  shellac. 


Fig.  SOO. 

In  the  Oraphophone  of  Bell  and  Tainter,  the  point  at- 
tached to  the  diaphragm  is  caused  to  cut  or  engrave  a  cylinder 
of  hardened  wax.  Two  separate  diaphragms  are  employed, 
one  for  speaking,  and  the  other  for  hearing. 

The  surface  is  made  of  a  mixture  of  beeswax  and  parafflne. 
A  uniformity  of  rotation  of  the  cylinder  is  obtained  by  means 


WORDS,  TERMS  AND  PHRASES. 


459 


Fig.  SOL 


460 


A  DICTIONARY  OF  ELECTRICAL 


of  a  motor  provided  with  a  suitable  governor.  An  ordinary 
conversation  of  some  five  minutes,  it  is  claimed,  can  be 
recorded  on  the  surface  of  a  cylinder  6  inches  long  and  \}^ 
inch  in  diameter. 

In  the  Gramophone  of  Berliner,  a  circular  plate  of  metal, 
covered  with  a  film  of  finely  divided  oil  or  grease,  receives  the 


record  in  a  sinuous,  spiral  line.  This  record  is  subsequently 
etched  into  the  metal  by  any  suitable  means,  or  is  photog- 
raphically reproduced  on  another  sheet  of  metal. 

Glass  covered  with  a  deposit  of  soot  is  sometimes  employed 
for  the  latter  process.  The  apparatus  is  shown  in  Fig.  302,  as 
arranged  for  the  reproduction  of  speech. 

In  Mr.  Berliner's  apparatus,  the  record  surface  is  impressed 
by  a  point  attached  to  the  transmitting  diaphragm,  in  a  direc- 
tion parallel  to  the  record  surface,  and  not,  as  in  the  instrument 


AVORDS,  TERMS  AND  PHRASES.  461 

of  Mr.  Edison,  in  a  direction  at  right  angles  to  the  same.  This 
method,  would  appear  to  be  the  best  calculated  for  the 
more  exact  reproduction  of  articulate  speech,  since  it  permits 
comparatively  loud  speaking  or  singing,  without  interfer- 
ing with  the  quality  of  the  reproduced  sounds.  Since  the  re- 
sistance to  indentation,  or  vertical  cutting,  increases  more 
rapidly  than  the  increase  in  the  amplitude  of  vibration  (See 
Amjrtitude  of  Vibration)  of  the  cutting  point,  it  follows  that 
the  louder  the  sounds  recorded  by  the  phonograph  or  grapho- 
phone,  the  less  complete  would  be  the  quality  of  the  repro- 
duced sounds,  or  the  less  the  probability  of  the  peculiarities 
of  the  speaker's  voice  being  recognized.  In  order  to  avoid 
this,  the  speaker  in  the  phonograph  and  the  graphophone 
speaks  in  an  ordinary  conversational  tone  only. 

For  purposes  of  dictation,  and  most  commercial  purposes, 
this  is  rather  an  advantage  than  otherwise. 

Phonograph,  Graphophonc,  or  Gramophone 
Records. — Records  produced  in  a  phonograph,  grapho- 
phone, or  gramophone,  for  the  subsequent  reproduction  of 
audible,  articulate  speech. 

Phonozcnograph.— An  instrument  devised  by  De  Feltre 
to  indicate  the  direction  of  a  distant  sound. 

A  Deprez-D' Arson val  galvanometer,  a  Wheatstone's  bridge, 
and  a  microphone  of  peculiar  construction,  are  placed  in  the 
circuit  of  a  voltaic  battery,  and  a  receiving  telephone.  The 
observer  determines  the  direction  of  the  distant  sound  by 
means  of  the  sounds  heard  under  different  conditions  in  the 
telephone. 

Phoiilotf  raph.— A  name  proposed  for  an  electro-thermal 
recording  telephone  devised  by  Irish. 

Phosphorescence.— The  power  of  emitting  light,  or  be- 
coming luminous  by  simple  exposure  to  light. 

Bodies  that  possess  the  property  of  phosphorescence,  when 
exposed  to  a  bright  light  acquire  the  power  of  continuing 


462  A  DICTIONARY  OP  ELECTRICAL 

to  emit  light,  when  carried  into  the  dark,  for  periods  varying 
from  a  few  seconds  to  several  hours.  The  diamond,  barium  and 
calcium  sulphides,  dry  paper,  silk,  sugar,  and  compounds  of 
uranium,  are  examples  of  phosphorescent  substances. 

A  phosphorescent  body  generally  emits  light  of  the  same 
character  as  that  it  absorbed  when  exposed  to  the  exciting 
light.  That  there  is  an  actual  absorption,  is  seen  from  the 
fact  that  the  light  which  has  passed  through  a  fluorescent 
solution,  fails  to  produce  fluorescent  effects  in  a  similar  solu- 
tion. A  selective  absorption  has,  therefore,  been  effected. 

The  effects  of  phosphorescence  appear  to  be  due  to  sympa- 
thetic vibrations  set  up  in  the  molecules  of  the  phosphores- 
cent body  by  the  exciting  light.  (See  Sympathetic  Vibrations.) 

In  some  cases,  however,  that  are  not  exactly  understood, 
the  wave  length  of  the  emitted  light  is  more  rapid  than  that 
.  of  the  exciting  light. 

The  phenomena  of  fluorescence  are  now  generally  believed 
to  be  due  to  the  phosphorescence  of  the  body  during  its  ex- 
posure to  the  light,  The  portions  traversed  by  the  light  are 
thus  temporarily  rendered  luminous.  (See  Fluorescence.} 

The  fire-fly,  the  glow-worm,  and  decaying  animal  or  vege- 
table matter,  exhibit  a  species  of  phosphorescence,  that  ap- 
pears to  be  due  to  the  actual  oxidation,  or  gradual  burning 
of  a  peculiar,  specific,  chemical  substance. 

Phosphorescence  may  therefore  be  divided  into  two  classes, 
viz.: 

(1)  Physical  Phosphorescence,  or  that  produced,  by  the 
actual  impact  of  the  light,  and, 

(3)  Chemical  Phosphorescence,  or  that  caused  by  an  actual 
chemical  combination,  or  the  combustion  of  a  specific  sub- 
stance. 

Phosphorescent  paints  for  rendering  the  position  of  a  push 
button,  electric  call,  match  safe,  or  other  similar  object  visible 
at  night,  consist  essentially  of  sulphides  of  calcium  or 
barium,  or  of  mixtures  of  the  same. 


WORDS,  TERMS  AND   PHRASES.  463 

Phosphorescence,  Electric Phospho- 
rescence caused  in  a  substance  by  the  passage  of  an  electric 
discharge. 

The  phosphorescent  material  is  placed  in  an  exhausted  glass 
tube,  as  shown  in  Fig.  303,  and  submitted  to  the  action  of  a 
series  of  discharges,  as  from  a  Ruhmkorff  coil,  or  Holtz 
machine.  The  violet  blue  light  of  such  discharge  is  very 
efficient  in  producing  phosphorescence.  Phosphorescence  is 
thus  effected  by  subjecting  the  phosphorescent  material  to 
the  molecular  bombardment  which  thus  occurs  in  a  high 
vacuum.  (See  Bombardment,  Molecular.) 

Photometer. — An  apparatus  for  measuring  the  intensity 
of  the  light  emitted  by  any  luminous  source. 

There  are  vari- 
ous methods  for 
measuring  the  in- 
tensity of  a  beam 
of  light  passing 
through  any  giv- 
en space,or  emitt- 
ed from  any  lum- 
inous  source; 
these  methods 
are  embraced  in  ^- 30Sf 

the  use  of  the  following  apparatus  : 

(1)  Calorimetric  Photometer,  in  which  the  light  to  be  meas- 
ured is  absorbed  by  the  face  of  a  thermo-electric  pile  and  the 
electric    current   thereby    produced    is   carefully    measured. 
Since  obscure  radiation,  or  heat  will  also  thus  produce  an 
electric  current,  it  is  necessary  to  first  absorb  all  the  heat  by 
passing  the  beam  of  light  through  an  alum  cell. 

(2)  Actinic,  or  Chemical  Photometers,  in  which  the  intensity 
of  the  light  is  estimated  by  a  comparison  of  the  depth  of 

oloration  product  on  a  fillet  of  photographic  paper  under 


464 


A  DICTIONARY  OF   ELECTRICAL 


similar  conditions  of  exposure  to  a  standard  light,  and  the 
light  to  be  measured. 

The  combination  of  pure  hydrogen  and  chlorine,  or  the  de- 
composition of  pure  mercurous  chloride,  have  been  employed 
for  the  purpose  of  determining  the  intensities  of  two  lights  by 
measuring  the  amount  of  chemical  decomposition  effected. 

(3)  Shadow  Photometers,  in  which  a  shadow  produced  by 
the  light  to  be  measured  is  compared  with  a  shadow  produced 
by  a  standard  candle,  (See  Candle,  Standard.) 


Fig.  SOL 

Rumford's  photometer,  shown  in  Fig.  304,  is  an  example 
of  this  form  of  instrument.  The  standard  candle,  shown  at  L, 
casts  a  shadow  C",  of  an  opaque  rod  C,  on  the  screen  at  B. 

The  light  to  be  measured  L',  is  moved  away  from  the  screen 
until  its  shadow  C',  on  the  screen  at  A,  is  judged  by  the  eye  to 
be  of  the  same  depth.  The  distance  between  the  screen  and 
the  lights  is  then  measured  in  straight  lines.  The  relative  in- 
tensities of  the  two  lights  are  then  proportional  to  the  squares 
of  their  d-istances.  If,  for  example,  the  candle  be  at  10  inches 


WORDS,  TERMS  AND  PHRASES.  465 

from  the  screen,  and  the  lamp  at  40  inches,  then  the  intensities 
are  as  10s  :  40s  or  as  100  :  1600,  or  the  lamp  is  a  16  candle-power 
lamp. 

This  photometer  is  based  on  the  fact  that  the  shadow  of  each 
source  is  illumined  by  the  light  of  the  other  source. 

(4)  Translucent  Disc  Photometers. — The  light  to  be  meas- 
ured and  a  standard  candle  are  placed  on  opposite  sides  of  a 
sheet  of  paper  the  centre  of  which  contains  a  grease  spot. 
The  standard  candle  is  kept  at  a  fixed  distance  from  the  paper 
and  the  other  light  is  moved  towards  or  from  the  paper 
until  both  sides  of  the  paper  are  judged  to  be  equally  illu- 
mined. 

In  Bunsen's  photometer  a  vertical  sheet  of  paper  with  a 
grease  spot  at  its  centre,  is  exposed  to  the  illumination  of  a 
standard  candle  on  one  side,  and  the  light  to  be  measured  on 
the  other. 

The  sheet  of  paper  is  placed  inside  a  dark  box  provided 
with  two  plane  mirrors  placed  at  such  an  angle  to  the  paper 
that  an  observer  can  readily  see  both  sides  of  the  paper  at  the 
same  time. 

This  box  can  be  slid  along  a  graduated,  horizontal  scale, 
towards,  or  from,  the  light  to  be  measured,  and  carries  with  it 
the  standard  candle  mounted  on  it  at  a  constant  distance  of  10 
inches.  If  the  box  is  too  near  the  light  to  be  measured,  the 
grease  spot  appears  brighter  on  the  side  of  the  sheet  of  paper 
nearest  the  candle.  If  too  near  the  candle,  it  appears  brighter 
on  the  side  of  the  sheet  of  paper  nearest  the  light  to  be 
measured.  The  position  in  which  the  spot  appears  equally 
bright  on  both  sides,  is  the  position  in  which  it  is  equally 
illumined,  and  the  relative  intensities  of  the  two  lights  are  then 
directly  as  the  squares  of  their  distances  from  the  sheet  of 
paper. 

Shadow,  and  translucent  disc,  photometers  being  dependent 
on  equal  illumination,  are  reliable  only  when  the  color  of  the 
lights  compared  is  the  same.  For  the  determination  of  the 


466  A  DICTIONARY   OF  ELECTRICAL 

photometric  intensity  of  very  bright  lights,  the  standard 
candle  is  replaced  by  a  carcel  lamp,  a  standard  gas  jet,  or  by 
the  light  emitted  by  a  given  mass  of  platinum,  heated  by  a 
given  current  of  electricity.  (See  Carcel  Lamp.  Carcel 
Standard  Gas  Jet.  Platinum  Standard  Light.) 

Preece's  photometer  belongs  to  the  class  of  translucent 
disc  photometers.  A  tiny  incandescent  lamp  is  placed  in  a 
box,  the  top  of  which  has  a  white  paper  screen  on  which  is 
a  grease  spot.  The  box  is  placed  in  the  street  where  the  in- 
tensity of  illumination  is  to  be  measured,  and  the  intensity  of 
the  light  of  tne  incandescent  lamp  is  varied  until  the  grease 
spot  disappears.  The  current  of  electricity  then  passing 
through  the  incandescent  lamp  acts  as  the  measure  of  the 
illumination. 

In  the  case  of  the  shadow  photometer,  or  of  Bunsen's  photo- 
meter, if  the  intensity  of  illumination  is  the  same,  the  relative 
intensities  of  the  two  lights  may  be  determined  as  follows  : 

Calling  I,  and  i,  respectively  the  relative  intensities  of  the 
standard  light,  and  the  light  to  be  measured,  and  D,  and  d, 
their  respective  distances  from  the  screen,  then 
I  :  i  :  :  D2  :  d*,  or  I  x  d*  =  i  x  D«; 

that  is,  i  =  I  (j^J  • 

Or,  the  intensity  of  the  light  to  be  measured  is  \ZTt)  times 

the  intensity  of  the  standard  light. 

If  for  example  D,  and  d,  represent  10  and  100  inches,  respec- 
tively, the  intensity  of  i  is  100  times  the  intensity  I,  the 
standard  light. 

(5)  Dispersion  Photometers. — A  class  of  photometers  in 
which,  in  order  to  more  readily  compare  or  measure  a  very 
bright  or  intense  light,  like  that  of  an  arc  lamp,  the  intensity 
of  the  light  is  decreased  by  dispersion  by  a  readily  measurable 
amount. 

Ayrton  &  Perry's  Dispersion  Photometer.— A  photometer 
in  which,  in  order  to  bring  an  intensely  bright  light,  like 


WORDS,  TERMS  AND  PHRASES.  467 

an  electric  arc  light,  to  such  an  intensity  as  will  permit  it  to 
be  readily  compared  with  a  standard  candle,  its  intensity 
is  weakened  by  its  passage  through  a  diverging  (concave) 
lens. 

Ayrton  &  Perry's  dispersion  photometer  is  shown  in  two 
different  positions,  Figs.  305  and  306.  The  apparatus  is 
supported  on  a  tripod  stand  E,  arranged  so  as  to  obtain 
exact  levelling.  A  plane  mirror  H,  movable  around  a  pin 
placed  directly  under  its  centre,  can  be  rotated  and  thus  reflect 
the  light  after  its  passage  through  the  diverging  Ions,  while 
still  maintaining  its  distance  from  the  electric  light. 


The  horizontal  axis  of  this  mirror  is  inclined  45°  to  its 
reflecting  surface  in  order  to  avoid  errors  arising  from  varying 
absorption  at  different  angles  of  reflection. 

The  inclination  of  the  beam  to  the  horizontal  is  indicated  by 
means  of  an  index  attached  to  the  mirror  and  moving  over 
the  graduated  circle  G. 

A  black  rod  A,  casts  its  shadow  on  a  screen  of  white  blot- 
ting paper  B.  A  standard  candle,  placed  in  the  holder  D, 


46o  A  DICTIONARY   OF  ELECTRICAL 

casts  its  shadow  alongside  the  shadow  cast  by  the  electric 
light.  The  lens  is  now  displaced  until  the  shadow  of  the 
electric  light  is  of  the  same  intensity  as  that  of  the  candle, 
when  viewed  successively  through  sheets  of  red  and  green 


A  graduated  scale  serves  to  mark  the  distance  of  the  candle 
and  of  the  lens  from  the  screen,  from  which  data  the  intensity 
of  the  electric  light  may  be  calculated. 


Fig.  306. 

(6)  Selenium  Photometers. — Instruments  in  which  the  rela- 
tive intensities  of  two  lights  are  determined  by  the  effects  pro- 
duced on  a  selenium  resistance. 

In  Siemens'  selenium  photometer  a  selenium  cell  is  em- 
ployed in  connection  with  an  electric  circuit  for  determining 
the  intensity  of  light. 

The  tube  A  B,  Fig.  307,  is  furnished  at  A  with  a  dia- 
phragm, and  at  B  with  a  selenium  plate,  connected  by  wires, 
G  G,  with  the  circuit  of  a  battery  and  a  galvanometer. 

A  graduated  scale  L  M,  bears  the  standard   candle    N. 


WORDS,  TERMS  AND  PHRASES. 


The  tube  A  B  is  capable  of  rotation  on  the  vertical  axis  F. 
A  reflecting  mirror-galvanometer  is  used  in  connection  with 
the  selenium  photometer.  The  light  to  be  measured  is 
placed  at  right  angles  to  the  scale  L  M,  and  the  tube  A  B 
directed  towards  it,  and  the  galvanometer  deflection  com- 
pared with  the  deflection  obtained  when  turned  towards  the 
standard  candle. 

(7)  Gas- Jet  Photometers. — Instruments  in  which  the  candle 
power  of  a  gas  jet  is  determined  by  measuring  the  height  at 
which  the  jet  burns  when  under  unit  conditions  of  volume 
and  pressure. 


Pig.  SOI. 

In  determining  the  candle  power  of  an  intense  light  like 
the  electric  arc  light,  a  large  gas  light  is  used  intsead  of  a 
standard  candle,  and  the  photometric  power  of  this  gas  light 
is  carefully  determined  by  comparison  with  a  gas-jet  pho- 
tometer. (See  Carcel,  Standard,  Gas  Jet.) 

Photoplionc. — An  instrument  invented  by  Bell  for  the 
telephonic  transmission  of  articulate  speech  along  a  ray  of 
light  instead  of  along  a  conducting  wire. 

A  beam  of  light,  reflected  from  a  diaphragm  against  which 


470  A  DICTIONARY  OF  ELECTRICAL 

the  speaker's  voice  is  directed,  is  caused  to  fall  on  a  Selenium 
resistance  inserted  in  the  circuit  of  a  voltaic  battery,  and  a 
telephone.  The  changes  thus  effected  in  the  resistance  of 
the  circuit  by  the  varying  amounts  of  light  reflected  on 
the  selenium  from  the  moving  diaphragm,  produce  in  the 
receiving  telephone,  a  series  of  to-and-fro  movements,  similar 
to  those  impressed  on  the  transmitting  diaphragm.  One 
listening  at  the  telephone  can  hear  whatever  has  been  spoken^ 
at  the  transmitting  diaphragm.  Telephonic  communication 
can  therefore. by  such  means  be  carried  on  along  a  ray  or 
beam  of  light,  theoretically  through  any  distance.  (See  Selen- 
ium, Resistance.) 

A  block  of  vulcanite  and  many  other  substances  may  be 
used  as  the  receiver,  since  it  has  been  discovered  that  a  rapid 
succession  of  flashes  of  light  produces  an  audible  sound  in 
small  masses  of  these  substances.  The  term  Sonorescence  has 
been  proposed  for  such  a  property.  (See  Sonorescence. ) 

Photophore,  Trouve's An  apparatus  in 

which  the  light  of  a  small  incandescent  electric  lamp  is  em- 
ployed for  purposes  of  medical  exploration. 

A  small  incandescent  lamp  is  placed  in  a  tube  containing  a 
concave  mirror  and  a  converging  lens. 

Phototelegraphy,  or  Telephotography.— The  elec- 
tric production  of  pictures,  writing,  charts,  or  diagrams  at  a 
distance.  (See  Telephotography.) 

Photo- Voltaic  Effect.— The  change  in  the  resistance  of 
selenium  or  other  substances  effected  by  their  exposure  to 
light.  (See  Selenium  Cell.) 

Physiology,  Electro (Sec  Electro-Physi- 
ology.) 

Piano,  Electric A  piano  in  which  the  strings 

are  struck  by  hammers  actuated  by  means  of  electro-mag- 
nets, instead  of  by  the  usual  mechanical  action  of  levers. 


WORDS,  TERMS  AND  PHRASES.  471 

Electric  piano-action  is  mainly  useful  in  permitting  the  in- 
strument to  be  played  at  any  distance  from  the  performer. 
It  is  also  of  value  from  the  ease  it  affords  in  recording  the 
piece  played. 

It  fails,  however,  to  properly  preserve  the  various  modula- 
tions of  force  so  requisite  for  brilliant  instrumentation. 

Pickle. — An  acid  solution  in  which  metallic  objects  are 
dipped  before  being  galvanized,  or  electroplated,  in  order  to 
thoroughly  cleanse  their  surfaces. 

The  pickle  used  for  the  preparation  of  iron  for  galvaniza- 
tion is  a  weak  solution  of  sulphuric  acid  in  water.  Vari- 
ous acids,  or  acid  liquids,  are  employed  for  that  thorough 
cleansing  of  metallic  surfaces  so  necessary  in  order  to  ensure 
an  even,  uniform,  adherent  coating  of  metal  by  the  process 
of  electro-plating.  (See  Electro-Plating.) 

Pile,  Dry A  voltaic  battery,  consisting  of 

numerous  voltaic  couples  formed  of  discs  of  paper  covered  on 
one  side  with  zinc-foil,  and  on  the  other  with  black  oxide  of 
manganese.  (See  Dry  Pile.) 

Pile,  Matteucci's  Muscular (See  Muscular 

Pile,  Matteucci's.) 

Pile,  Tliermo-Electric A  battery  consisting 

of  a  number  of  thermo-electric  couples  connected  so  as  to 
form  a  single  electric  source.  (See  Thermo-Electric  Battery.) 

Pile,  Voltaic A  battery  consisting  of  a 

number  of  voltaic  couples  connected  so  as  to  form  a  single 
electric  source. 

A  form  similar  to  Volta's  original  pile,  consisting  of  alternate 
discs  of  copper  and  zinc,  separated  from  each  other  by  discs  of 
wet  cloth,  and  piled  on  one  another,  so  as  to  form  a  number  of 
separate  voltaic  couples  connected  in  series,  is  shown  in 
Fig.  308.  The  thick  plates  marked  Zra,  are  of  zinc;  the 
copper  plates,  marked  CM  are  much  thinner.  The  discs 
of  moistened  cloth  are  shown  at  d  d.  One  end  of  such  a 


472 


A  DICTIONARY   OF   ELECTRICAL 


pile,  would  then  be  terminated  by  a  plate  of  copper,  and  the 
other  by  a  plate  of  zinc.  The  copper  end  forms  the  positive 
electrode,  and  the  zinc  end  the  negative  electrode.  (See  Cell, 
Voltatic,  Polarity  of  Electrodes.) 

Pi  III.— A  light,  cellular  ma- 
terial forming  the  central  por- 
tions of  most  exogenous  plants. 
An  excellent  pith,  suitable  for 
electrical  purposes,  is  furnished 
by  the  dried  wood  of  the  elder- 
berry. 

Pith-Ball  Electroscope. 
— An  electroscope  which  shows 
the  presence  of  a  charge  by 
the  repulsion  of  two  similarly 
charged  pith  balls.  (See  Elec- 
troscope.) 

Any  two  pith  balls,  suspended 
by  conducting  threads,  but  in- 
sulated from  the  earth,  will 
serve  as  an  electroscope. 

Pith  Balls.— Two  balls  of 
pith,  suspended  by  conducting 
threads  of  cotton  to  insulated 
conductors,   and    employed  to 
show  the  electrification  of  the 
same,by  their  mutual  repulsion. 
The  pith  balls  connected  with 
.  308.  the    insulated    cylinder    A    B, 

Fig.  309,  not  only  show  the  electrification  of  the  cylinder,  but 
serve  also  to  roughly  indicate  the  peculiarities  of  distribution 
of  the  charge  thereon. 

Pivot  Suspension.— The  suspension  of  a  needle  or  mag- 
net, by  a  pivot,  as  distinguished  from  suspension  by  a  thread. 
(See  Suspension,  Methods  of.) 


WORDS,  TERMS  AND  PHRASES.  473 

Plants,  Electricity  of  —  — Electricity  produced 
naturally  by  plants  during  their  vigorous  growth. 

DuBois-Reymond  and  others,  have  shown  that  plants  while 
in  a  vigorous  vital  state,  are  active  sources  of  electricity.  If 
one  of  the  terminals  of  a  galvanometer  be  inserted  into  a  fruit 
near  its  stem,  and  the  other  terminal  into  the  opposite  part  of 
the  fruit,  the  galvanometer  at  once  shows  the  presence  of  an 
electric  current. 

Buff  has  shown  that  the  roots  and  interior  portions  of  plants 
are  always  negatively  charged,  while  the  flowers,  fruits  and 
green  twigs  are  positively  charged. 

Plant  tissue  or  fibre,  like  the  muscular  fibre  of  animals, 
exhibits  in  many  cases  a  true  contraction  on  the  passage 
through  it  of  an  electric  current.  This  is  seen  in  the  mimosa 
sensitiva,  or  sensitive  fern ;  in  the  Venus'  fly  trap ;  and  in 
several  other  species  of  plants. 


Plate  Condenser.— (See  Condenser  or  Accumulator.) 

Plating  Bath,  Electro (See  Bath,  Electro- 
Plating.) 

Plating,  Electro The  depositing  of  a  plating 

or  coating  of  one  metal  on  the  surface  of  another  metal,  or  on 
any  conducting  surface,  by  the  action  of  electricity. — (See 
Electro-Plating.) 

Platinoid. — An  alloy  consisting  of  German  silver  with 
one  or  two  per  cent,  of  metallic  tungsten. 


474  A  DICTIONARY  OF  ELECTRICAL 

This  alloy  is  suitable  for  use  in  resistance  coils  on  account 
of  the  comparatively  small  influence  produced  on  its  electric 
resistance  by  changes  of  temperature.  (See  Coils,  Resistance), 

Its  resistance  is  60  per  cent,  higher  than  that  of  German 
silver. 

Platinum. — A  refractory  and  not  readily  oxidizable  metal, 
of  a  tin  white  color. 

The  coefficient  of  expansion  of  platinum  by  heat  is  nearly 
that  of  ordinary  glass.  Platinum  is,  therefore,  much  employed 
for  the  leading-in  conductors  of  an  incandescent  lamp. 

Platinum  Black.— Finely  divided  platinum  that  pos- 
sesses, in  a  marked  degree,  the  power  of  absorbing  or  occlud- 
ing gases. 

Platinum  black  is  obtained  by  the  action  of  potassium  \\y- 
drate  on  platinum  chloride.  Unlike  metallic  platinum  it  is  of 
a  black  color. 

Platinum-Silver  Alloy.— An  alloy  used  for  resistance 
coils,  consisting  of  one  part  of  platinum  and  two  parts  of  silver. 

Platinum  Standard  Light.— The  light  emitted  by  a 
surface  of  platinum,  one  square  centimetre  in  area,  at  its  tem- 
perature of  fusion. 

Plow. — The  sliding  contacts  connected  to  the  motor  of  an 
electric  streetcar,  and  placed  within  the  slotted  underground 
conduit,  and  provided  for  the  purpose  of  taking  off  the 
current  from  the  electric  mains  placed  therein,  as  the 
contacts  are  pushed  forwards  over  them  by  the  motion  of 
the  car. 

Similar  contacts,  placed  in  the  rear  of  the  motor  car  and 
drawn  after  the  train,  form  what  is  technically  known  as  the 
sled,  or  when  rolling  on  overhead  wires  as  trolleys,  (See  Rail- 
ways, Electric.) 

Plow,  Electric A  plow  driven  by  an  electric 

motor  placed  either  on  a  wagon  to  which  the  plow  is  attached, 


WORDS,  TERMS  AND  PHRASES.  475 

or  by  a  stationary  electro  motor,  by  the  aid  of  cords  or  other 
flexible  belts. 

One  of  the  first  practical  applications  of  the  electric  trans- 
mission of  energy  was  for  the  operation  of  a  plow,  driven 
electrically,  by  an  electric  current  generated  at  some  distance, 
and  transmitted  to  the  field  by  suitable  conductors. 

Pliicker  Tubes. — (See  Tubes,  Plucker.) 
Plug,  Infinity (See  Infinity  Plug.) 

Plumbago. — An  allotropic  modification  of  carbon. 

Plumbago,  the  material  commonly  known  as  black  lead,  is 
the  same  as  graphite.  Powdered  plumbago  is  employed  in 
electrotyping  processes  for  rendering  non-conducting  surfaces 
electrically  conducting.  For  this  purpose  powdered  plumbago 
is  dusted  on  the  surfaces  which  thus  acquire  the  power  of  re- 
ceiving a  metallic  lustre  by  friction.  Stove  polishes  are 
formed  of  mixtures  of  plumbago  and  other  cheaper  materials. 
(See  Graphite.) 

Strictly  speaking  the  term  graphite  is  properly  applied  to 
such  varieties  of  plumbago  as  are  suitable  for  direct  use  for 
writing  purposes  as  in  lead  pencils. 

Plunge  Battery.— (See  Battery,  Plunge.) 
Pneumatic  Perforator. — (See  Perforator,  Pneumatic.) 

Pneumatic    §ignal§,   Electro    -  —(See 

Signals,  Electro-Pneumatic.) 

Poggendorff's  Voltaic  Cell.— (See  Cell,  Voltaic.) 

Point§,  Electric  Action  of The  effect  of  points 

placed  on  an  insulated,  charged  conductor,  is  to  slowly  dis- 
charge the  conductor  by  electric  convection.  (See  Convection, 
Electric.) 

The  cause  of  this  action  is  the  increased  density  of  a  charge 
on  the  surface  of  a  conductor  in  the  neighborhood  of  points. 
(See  Charge,  Distribution  of.) 


476  A  DICTIONARY  OF  ELECTRICAL 

Points  or  Rhumbs,  of  Compass.— The  thirty-two 
points  into  which  a  compass  card  is  divided. 

Sixteen  of  these  points  are  shown  in  Fig.  310.  The  position 
of  the  remaining  will  be  readily  seen  by  an  inspection  of  the 
figures. 

These  points  are  as  follows  : 

1.  North.  17.  South. 

2.  N.  by  E.  18.  S.  by  W. 

3.  N.  N.  E.  19.  S.  S.  W. 

4.  N..E.  byN.  20.  S.  W.  by  S. 

5.  N/E.  21.  S.  W. 

6.  N.  E.  by  E.  22.  S.  W.  W. 

7.  E.  N.  E.  23.  W.  S.  W. 

8.  E.  by  N.  24.  W.  by  S. 

9.  East.  25.   West. 

10.  E.  by  S.  26.  W.  by  N. 

11.  E.  S.  E.  27.  W  N.  W. 

12.  S.  E.  by  E.  28.  N.  W.  by  W. 

13.  S.  E.  29.  N.  W. 

14.  S.  E.  by  S.  30.  N.  W.  by  N. 

15.  S.  S.  E.  31.  N.  N.  W. 

16.  S.  by  E.  32.  N.  by  W. 
Boxing  the  Compass,  consists  in  naming  all  these  points  con- 
secutively from  any  one  of  them. 

The  direction  in  which  the  ship  is  sailing  is  determined  by 
means  of  a  point  fixed  on  the  inside  of  the  compass  box, 
directly  in  the  line  of  the  vessel's  bow. 

Points  on  Lightning  Rod.— Points  of  inoxidizable 
material,  placed  on  lightning  rods,  to  effect  the  quiet  discharge 
of  a  cloud  by  convection  streams.  (See  Lightning  Rods. 
Convection,  Electric.) 

Polarity,  Diamagnetic  —  —A  polarity,  the  re- 

verse of  ordinary  magnetic  polarity,  assumed  by  Faraday  to 
explain  the  phenomena  of  diamagnetism.  (See  Diamagnet- 
ism.) 


WORDS,  TERMS  AND  PHRASES. 


477 


Faraday  assumed  that  diamagnetic  substances,  when  brought 
into  a  magnetic  field,  such,  for  example,  as  north,  acquired 
north  magnetism  in  those  parts  that  were  nearest  the  north 
pole,  instead  of  south  magnetism  as  with  ordinary  magnetic 


substances.  The  north  pole  thus  obtained, 
explain  the  apparent  repul- 
sion of  a  slender  rod  of  any 
diamagnetic  material,  deli- 
cately suspended  in  a  strong 
magnetic  field,  and  cause  it 
to  point  equatorially,  or  with 
the  lines  of  force  passing 
through  its  least  dimen- 
sions. This  supposition  was 
subsequently  abandoned  by 
Faraday.  It  has  recently 
been  revived  by  Tyndall. 
(See  Diamagnetic.) 
Polarity,  Magnetic 


rould,  he  thought, 


S 

Fig.  310. 

The  polarity  acquired  by  a  magnetizable  substance 

when  brought  into  a  magnetic  field. 

The  direction  of  magnetic  polarity,  acquired  by  a  substance 
when  brought  into  a  magnetic  field,  depends  on  the  direction  in 
which  the  lines  of  magnetic  force  pass  through  it.  Where 
these  lines  enter  the  substance  a  south  pole  is  produced,  and 
where  they  pass  out,  a  north  pole  is  produced.  The  axis  of 
magnetization  lies  in  the  direction  of  the  lines  of  force  as  they 
pass  through  the  body,  and  the  intensity  of  magnetization, 
depends  on  the  number  of  these  lines  of  force. 

The  cause  of  magnetic  polarity  is  not  definitely  known. 
Hughes's  hypothesis  attributes  it  to  a  property  inherent  in  all 
matter.  Ampere  attributes  it  to  closed  electric  circuits  in 
the  ultimate  particles.  Whatever  its  cause,  it  is  invariably 
manifested  by  a  magnetic  field,  the  lines  of  force  of  which  are 
assumed  to  have  the  direction  already  mentioned. 


478  A  DICTIONARY  OF  ELECTRICAL 

Polarization  of  Dielectric.— A  molecular  strain  pro- 
duced in  the  dielectric  of  a  Leyden  jar,  by  the  attraction  of  the 
electricities  on  its  opposite  faces,  or  by  electrostatic  stress. 
(See  Dielectric  Strain.) 

The  polarization  of  the  glass  of  a  Leyden  jar,  and  the  ac- 
companying strain,  are  seen  by  the  frequent  piercing  of  the 
glass,  and  by  the  residual  charge  of  the  jar.  (See  Charge, 
Residual) 

Polarization  of  Electrolyte.— The  formation  of  mole- 
cular groups  or  chains,  in  which  the  poles  of  all  the  molecules 
of  any  chain  are  turned  in  the  same  direction,  viz. ,  with  their 
positive  poles  facing  the  negative  plate,  and  their  negative 
poles  facing  the  positive  plate.  (See  Cell,  Voltaic.  Grothuss* 
Hypothesis.) 

Polarization  of  Nerves. — (See  Electrotonus.) 

Polarization  of  Voltaic  Cell.— The  collection  of  a 
gas,  generally  hydrogen,  on  the  surface  of  the  negative  ele- 
ment of  a  voltaic  cell. 

The  collection  of  a  positive  substance  like  hydrogen  on  the 
negative  element  or  plate  of  a  voltaic  cell,  sets  up  a  counter 
electromotive  force,  which  tends  to  produce  a  current  in  the 
opposite  direction  to  that  produced  by  the  cell,  and  thus  to 
decrease  the  normal  current  of  the  cell.  (See  Counter  Elec- 
tromotive Force.) 

The  causes  of  the  decrease  of  the  normal  current  of  a  vol- 
taic cell  by  its  polarization,  are  as  follows  : 

(1)  The  Increased  Resistance  of  the  cell  owing  to  the  bubbles 
of  gas,  which  form  part  of  the  circuit. 

(2)  The  Counter  Electromotive  force,  produced  by  the  film 
of  gas  on  the  negative  plate. 

There  are  three  ways  in  which  the  ill  effects  of  this  polariz- 
ation can  be  avoided.  These  are  : 

(1)  Mechanical. — The  negative  plate  is  furnished  with  a 
roughened  surface  which  enables  the  bubbles  of  gas  to  escape 


WORDS,  TERMS  AND  PHRASES.  <J79 

from  the  points  on  such  surface ;  or,  a  stream  of  gas,  or  air, 
is  blown  through  the  liquid  against  the  plate  to  brush  the 
bubbles  off. 

(2)  Chemical— The  surface  of  the  negative  plate  is  sur- 
rounded by  some   powerful    oxydizing  substance,   such    as 
chromic  or  nitric  acid,  which  is  capable  of  oxidizing  the  hy- 
drogen, and  thus  thoroughly  removing  it  from  the  plate.  The 
oxidizing  substance  may  form  the  entire  electrolyte,  as  is  the 
case  of  the  bichromate  solution  employed  in  the  zinc-carbon 
couple.     Generally,  however,  it  has  been  found  preferable  to 
employ  a  separate  liquid,  like  nitric  acid  to  completely  sur- 
round the  negative  plate,  and  another  liquid  for  the  positive 
plate,  the  two  liquids  being  generally  kept  from  mixing  by  a 
porous  cell,  or  diaphragm.     Such  cells  are  called  double  fluid 
cells.    (See  Cell,  Voltaic,  Double  Fluid.) 

(3)  Electro  Chemical. — This  also  necessitates  a  double  fluid 
cell.     The  negative  element  is  immersed  in  a  solution  of  a 
salt  of  the  same  metal  as  the  negative  plate.     Thus,  a  copper 
plate,   immersed  in  a  solution  of  copper  sulphate,   cannot 
be  polarized  since  metallic  copper  is  deposited  on  its  sur- 
face by  the  action  of  the  hj'drogen  which  tends  to  be  liberated 
there.     The  constancy  of  action  of  a  Daniell  cell    depends  on 
a  deposition    of    metallic    copper    on    its    copper    plate    as 
well  as  on  the  formation  of  hydrogen  sulphate,   and   the 
solution  of  additional  copper  sulphate.     (See   Cell,   Voltaic, 
DanieWs.) 

Polarized  Armature.— (See  Armature,  Polarized.) 
Polarized  Relay. — (See  Relay,  Polarized.) 

Pole,  Antilogous  —  —That  pole  of  a  pyro-electric 
substance,  like  tourmaline,  which  acquires  a  negative  electrifi- 
cation when  the  temperature  is  rising,  and  a  positive  electrifi- 
cation when  it  is  falling,  (See  Pyro-  Electricity.) 

Pole  (Jhauger. — A  switch  or  key  for  changing  or  revers- 


480  A  DICTIONARY   OF  ELECTRICAL 

ing  the  direction  oi  current  produced  by  any  electric  source, 
such  as  a  battery. 

The  commutator  of  a  Ruhmkorff  coil  is  a  simple  form  of 
pole  changer.  (See  Induction  Coils.) 

Pole  Pieces. — Pieces  of  soft  iron  placed  at  the  ends  of 
the  poles  of  electro  magnets  for  the  purpose  of  concentrating 
and  directing  their  magnetic  fields. 

Pole  Pieces  of  Dynamos. — Masses  of  iron  connected 
with  the  poles  of  the  field  magnet  frames  of  dynamo-electric 
machines,  and  shaped  to  conform  to  the  outline  of  contour 
of  the  armature. 

The  pole  pieces  are  made  in  a  variety  of  forms,  but  in  all 
cases  are  so  shaped  as  to  conform  to  the  outline  of  the  space 
in  which  the  armature  rotates. 

They  are  brought  as  near  as  possible  to  the  armature  so  as 
to  increase  the  intensity  of  the  magnetic  induction.  The  in- 
tervening air  space  should  be  as  thin  as  possible,  but  of  as 
large  an  area  as  convenient. 

The  opposite  pole  pieces  should  not  have  their  extensions 
brought  too  near  together,  as  this  will  permit  of  serious  loss 
through  magnetic  leakage.  The  distance  between  them 
should  be  as  many  times  the  depth  of  the  armature  windings 
as  possible.  (See  Magnetic  Leakage.) 

Rounded  edges  are  preferable  to  sharp  edges  for  the  same 
reason. 

Poles,  Consequent of  Magnet.— (See  Con- 
sequent Magnet  Poles.) 

Poles,  False (See  False  Poles.) 

Poles  of  magnetic  Intensity.— The  earth's  magnetic 
poles  as  determined  by  means  of  the  needle  of  oscillation. 

The  points  of  the  earth's  greatest  magnetic  intensity.  (See 
Inclination  Chart.) 

Poles  of  Verticity,  Magnetic.— The  earth's  magnetic 
poles  as  determined  by  means  of  the  dipping  needle, 


WORDS,  TERMS  AND   PHRASES.  481 

The  points  of  the  north  where  the  angle  of  dip  is  90°.  (See 
Inclination  Chart.) 

Poles,  Telegraphic Wooden  or  iron  uprights  on 

which  telegraphic  or  other  wires  are  hung. 

Wooden  poles  are  generally  round. 

The  terminal  pole,  or  the  last  pole  at  each  end  of  the  line, 
or  where  the  wires  bend  at  an  angle  of  nearly  90°,  is  gener- 
ally cut  square. 

The  holes  for  the  poles  must  be  dug  in  the  true  line  of  the 
wires,  and  not  at  an  angle  to  such  line.  As  little  ground 
should  be  disturbed  in  the  digging  as  possible.  Earth  borers, 
or  modifications  of  the  ordinary  ship  auger,  are  generally 
employed  for  this  purpose.  When  the  pole  is  placed  in  posi- 
tion the  ground  should  be  rammed,  or  punned  around  the 
pole. 

In  setting  the  pole,  it  is  generally  set  at  least  five  feet  in 
the  ground.  In  England  the  poles  are  planted  to  a  depth  of 
about  one-fifth  of  their  length.  In  embankments  and  loose 
ground,  they  are  planted  deeper  than  in  more  solid  earth.  On 
curves,  the  poles  should  be  inclined  a  little  so  as  to  lean  back 
against  the  lateral  strain  of  the  wire,  since  by  the  time  the 
ground  has  completely  set,  the  strain  of  the  wire  will  have 
pulled  them  into  an  erect  position. 

Care  must  be  taken  to  so  plant  the  poles  on  that  side  of  a  road 
or  railway,  that  the  prevailing  winds  will  blow  them  off  the 
same,  should  it  overturn  them.  As  to  location,  the  top  of 
steep  cuttings  is  preferable  to  the  slope.  In  all  exposed  posi- 
tions, it  is  preferable  to  strengthen  the  poles  by  stays  attached 
to  both  sides. 

Where  the  number  of  wires  is  unusually  large,  heavy 
timber,  or  in  case  of  its  absence,  double  poles  suitably  braced 
together,  must  be  employed.  In  long  lines  the  poles  should 
all  be  numbered  in  order  to  afford  ease  for  reference  or  repair. 

When,  even  with  the  best  punning,  and  other  precautions, 
the  pole  is  judged  to  be  unable  to  resist  the  strain  on  it,  stays 


A  DICTIONARY   OF  ELECTRICAL 


and  struts  are  employed.  A  stay  is  used  when  it  is  desired  to 
remove  the  pull  or  tension  from  the  pole ;  a  strut,  when  it  is 
desired  to  remove  the  thrust  or  pressure. 


Fig.  Sll. 

The  arms  or  brackets,  or  the  cross  pieces  that  support  the 
insulators,  should  all  be  placed  on  the  same  side  of  the  poles. 
Some  common  forms  of  arms  or  brackets  are  shown  in 
Fig.  811. 

Saddle  Brackets  should  be  placed  on  alternate  sides  of  the 
pole.    When  the  strain  on  an  insulator  is  too  great,  on  ac- 
count  of    the    wire 
going  off  at  a  sharp 
angle,   a  Shackle  is 
used.    This  is  a  spec- 
ial form  of  insulator 
which   confines   the 
ff-  312.  strain  to  one  spot. 

A  form  of  Double  Shackle  is  shown  in  Fig.  312.     The  wire 
passes  around  the  recess  at  B,  between  the  two  insulators. 
On  curves,  or  in  any  situation  when  there  is  a  probability,  in 


WORDS.  TERMS  AND  PHRASES. 


483 


case  of  the  breaking  of  an  insulator,  of  a  wire  getting  into  a 
dangerous  position  Guards  should  be  employed. 

Guards  are  of  two  kinds,  viz.:  Hoop  Guards  and  Hook 
Guards.  A  form  of  hook  guard  is  shown  in  Fig.  313. 

When  wooden  poles  are  employed  various  preservative 
methods  are  adopted  to  protect  the  wood  from  decay,  which  is 
very  apt  to  occur,  especially  at  the  line  of  the  pole  enters  the 
ground.  Some  of  these  forms  are  as  follows,  viz. : 

(1)  Charring   and   Tarring  the  ^^.^ 
butt  end  of  the  pole  where  it  en-        /^^    G 
ters  the  ground,  so  as  to  expel  the 

sap  and  destroy  injurious  plants  or 
animal  germs. 

The  charred  end  is  then  cleansed 
and  dipped  in  a  mixture  of  tar  and 
slaked  lime. 

(2)  Burnetising,  or  the  introduc- 
tion of  chloride  of  zinc  into  the 
pores  of  the.wood,  by  placing  the 
poles  in  an  open  tank  filled  with  a 
solution  of  this  salt. 

(3)  Kyanising,  or  the  similar  in- 
troduction of  corrosive  sublimate, 
or  mercuric  chloride. 

(4)  Boucher -ising,  or  the  injection  of  a  solution  of  copper  sul- 
phate, into  the  pores  of  the  wood. 

(5)  Creosoting,   or  the   application  of  creosote  to  well -sea- 
soned poles. 

Porous  Cells. — Jars  of  unglazed  earthenware,  employed 
in  double-fluid  voltaic  cells,  to  keep  the  two  liquids  separated. 

The  use  of  a  porous  cell  necessarily  increases  the  internal 
resistance  of  the  cell,  from  the  decrease  it  produces  in  the  area 
of  cross  section  of  liquid  between  the  two  elements.  When 
the  battery  is  dismantled,  the  porous  cells  should  be  kept  u  nder 
water,  otherwise  the  crystallization  of  the  zinc  sulphate  or 


484 


A  DICTIONARY  OF  ELECTRICAL 


other  salt  is  apt  to  produce,  serious  exfoliation,  or  even  to 
crumble  the  porous  cell. 

A  porous  cell  is  sometimes  called  a  diaphragm.  (See  Cell, 
Voltaic.) 

Portative  Power.— The  lifting  power  of  a  magnet. 
(See  Lifting  Power  of  Magnet.) 


fig.  SlU. 

Portrait,  Electric A  portrait  formed  on  paper  by 

the  electric  volatilization  of  gold  or  other  metal. 

An  electric  portrait,  is  obtained  by  cutting  on  a  thin  card  a 
portrait,  in  the  form  of  a  stencil.  A  sheet  of  gold  leaf  is  then 
placed  on  one  side  of  the  paper  stencil,  and  a  sheet  of  paper 
on  the  other  side ;  sheets  of  tin  foil  are  then  placed  on  the 
outside,  as  shown  in  Fig.  314,  and  the  whole  firnr^y  p"essed 


WORDS,  TERMS  AXD  PHRASES.  485 

together.  If  now  a  disruptive  discharge  is  passed  through 
from  one  sheet  of  tin  foil  to  the  other,  the  gold  leaf  is  vo- 
latilized, and  a  purplish  stain  is  left  on  the  paper  on  the 
outlines  of  the  stencilled  card,  thus  forming  an  electric  por- 
trait. 

Positive  Electricity.— One  of -the  phases  of  electrical 
excitement,  rather  than  one  of  the  kinds  of  electricity.  (See 
Negative  Electricity.) 

Positive  Direction  of  Lines  of  magnetic  Force. 
— The  direction  the  lines  of  magnetic  force  are  assumed  to 
take,  viz. :  out  of  the  north  pole  of  a  magnet  and  into  the  south 
pole.  (See  Field,  Magnetic.  Direction  of  Lines  of  Force.) 

Posts,  Binding or  Binding  Screws.— (See 

Binding  Posts.) 

Potential,  Constant -A  potential  which  remains 

constant  under  all  conditions. 

A  machine  or  other  electric  source  is  said  to  have  a  con- 
stant potential  when  it  is  capable,  while  in  operation,  of  main- 
taining a  constant  difference  of  electric  pressure  between  its 
two  terminals.  (See  Circuit,  Constant  Potential.) 

Potential,  Difference  of  — (See  Difference 

of  Potential) 

Potential,  Difference  of Methods  of  meas- 
uring   —Methods  employed  for  determin- 
ing difference  of  potential. 

These  methods  are  as  f  ollowrs  : 

(1)  By  the  Method  of  Weighing,  that  is,  by  obtaining  the 
weight  required  to  overcome  the  attraction  between  two  op- 
positely charged  plates,  or  oppositely  energized  coils ;  or  by 
measuring  the  repulsion  between  similarly  charged  surfaces, 
or  similarly  energized  coils. 

(2)  By  the  use  of  Electrometers,  or  apparatus  designed  for 
measuring  differences  of  potential.     (See  Electrometers.) 

(3)  By  the  use  of  Galvanometers. 


486  A  DICTIONARY  OF  ELECTRICAL 

Difference  of  potential,  in  the  case  of  currents,  may  be 
determined  from  the  quantity  of  electricity  which  flows  per 
second  through  a  given  circuit,  that  is,  by  the  number  of 
amperes,  just  as  the  pressure  of  water  at  any  point  in  the  side 
of  a  containing  vessel  can  be  determined  by  the  quantity  of 
water  that  flows  per  second.  Difference  of  potential  in  the 
case  of  currents,  therefore,  may  be  measured  by  any  galvano- 
meter which  measures  the  current  directly  in  amperes,  and 
knowing  the  resistance  of  the  circuit. 

Potential,  Electric The  power  of  doing 

electric  work. 

Electric  level. 

Electric  potential  can  be  best  understood  by  comparison 
with  the  case  of  a  liquid  such  as  water. 

The  ability  of  a  water  supply  or  source  to  do  work  depends: 

(1)  On  the  Quantity  of  Water. 

(2)  On  the  Level  of  the  Water,  as  compared  with  some  other 
level,  or,  in  other  words  on  the  difference  between  the  two 
levels. 

In  a  like  manner  the  ability  of  electricity  to  do  work  de- 
pends : 

(1)  On  the  Quantity  of  Electricity. 

(2)  On  the  Electric  Potential  at  the  place  where  the  elec- 
ricity  is  produced,  as  compared  with  that  at  some  other  place, 

r,  in  other  words  on  the  Difference  of  Potential. 

In  the  case  of  water  flowing  through  a  pipe,  the  quantity 
which  passes  in  a  given  time  is  the  same  at  any  cross  section  of 
the  pipe. 

In  the  case  of  electricity,  the  quantity  of  electricity  flowing 
through  any  conductor,  or  part  of  a  circuit,  is  the  same  at  any 
cross  section.  A  galvanometer  introduced  into  a  break  in  any 
part  of  the  conductor  would  show  the  same  strength  of 
current. 

But,  though  the  quantity  of  water  which  passes  is  the  same 
at  any  cross  section  of  a  pipe,  the  pressure  per  square  inch  is 


WORDS,  TERMS  AND  PHRASES. 


487 


not  the  same,  even  in  the  case  of  a  horizontal  pipe  of  the  same 
diameter  throughout,  but  becomes  less,  or  suffers  a  loss  of 
head,  or  difference  of  pressure,  at  any  two  points  along  the 
pipe,  that  causes  the  flow  between  these  two  points  against 
the  resistance  of  the  pipe. 

So  too,  in  the  case  of  a  conductor  carrying  an  electric  cur- 
rent, though  the  quantity  of  electricity  that  passes  is  the  same 
at  all  cross  sections,  the  electric  pressure  or  potential  is  by  no 
means  the  same  at  all  points  in  the  conductor,  but  suffers  a 
loss  of  electric  head  or  level  in  the  direction  in  which  the 
electricity  is  flowing.  It  is  this  loss  of  electric  head  or  level,  or 
difference  of  electric  potential,  that  causes  the  electricity 
to  flow  against  the  resistance  of  the  conductor. 


m 

f 

:• 

a' 

\ 

b' 

r- 

c 

j 

--. 

.- 

>c 

e' 

*f 

: 

a 

ft 

-  d 

-  e 

-.f 

"•" 

B 

^->s 

A 

Fig.  315. 

These  analogies  can  be  best  shown  by  the  following  illus- 
tration : 

In  Fig.  315,  a  reservoir,  or  source  of  water,  at  C,  communi- 
cates with  the  horizontal  pipe  A  B,  furnished  with  open 
vertical  tubes  at  a,  b,  c,  d,  e,  f,  g,  and  B.  If  the  outlet  at  B  is 
closed,  the  level  of  the  water  in  the  communicating  vessels 
is  the  same  as  at  the  source  ;  but  if  the  liquid  escape  freely 
from  B,  the  level  of  the  water  in  the  branch  pipes,  will  be 
found  on  the  inclined  dotted  line  or  at  a',  6',  c',  d',  e',  f,  g1, 
or  on  the  hydraulic  gradient. 


488 


A  DICTIONARY  OF  ELECTRICAL 


The  pressure  per  square  inch,  at  any  cross  section  of  the 
horizontal  pipe,  which  is  measured  by  the  height  of  the  liquid 
in  the  vertical  pipe  at  that  point,  decreases  in  the  direction  in 
which  the  liquid  is  flowing.  The  force  that  urges  the  liquid 
through  the  pipe  between  any  two  points,  may  be  called  the 
liquid-motive  force  (Fleming)  and  is  measured  by  the  differ- 
ence of  pressure  between  these  points. 

In  Fig.  316,  the  dynamo  electric  machine  at  D,  has  its  nega- 
tive pole  grounded,  and  its  positive  pole  connected  to  a  long 
lead,  A  B,  the  postive  end  of  which  is  also  grounded.  A  fall 
of  potential,  represented  by  the  inclined  dotted  line,  occurs  be- 
tween A  and  B,  in  the  direction  in  which  the  electricity  is  flow- 

™9' 

"fVc, 


fig.  316. 

The  dynamo  electric  machine  may  be  regarded  as  a  pump 
that  is  raising  the  electricity  from  a  lower  to  a  higher  level, 
and  passing  it  through  the  lead  A  B.  The  electric  pressure  or 
potential  producing  the  flow  is  greatest  near  the  dynamo  and 
least  at  the  further  end,  the  differences  at  the  points  a,  b,  c, 
d,  e,  f,  and  g,  being  represented  by  the  vertical  lines  a  a',  b  b', 
c  c',  d  d',  e  e',  ff,  and  g  g'. 

The  electricity  flows  between  any  two  points  as  a,  and  b, 
in  the  conductor  A  B,  in  virtue  of  the  difference  of  electric 
pressure  or  potential  between  these  two  parts,  or  the  differ- 
ence between  a  a',  and  b  b'. 

Differences  of  potential  must  be  distinguished  from  differ- 


WORDS,  TERMS  AND  PHRASES.  489 

ences  in  electric  charge,  or  electrostatic  density.  If  two  con- 
ductors at  different  potentials  are  connected  by  a  conductor, 
a  current  will  flow  through  this  conductor.  When  their 
potential  is  the  same  no  current  flows.  The  density  of  a 
charge  is  the  quantity  of  electricity  per  unit  of  area. 

The  electric  potential  is  the  same  at  all  points  of  an  insulated 
charged  conductor ;  the  density  is  different  at  different  points, 
except  in  the  case  of  a  sphere.  The  potential,  however,  is  the 
same,  since  no  current  flows,  or  the  charge  does  not  redistribute 
itself .  The  density  on  an  insulated,  isolated  sphere  is  uniform 
over  all  parts  of  the  surface,  and  its  potential  is  the  same  at  all 
points.  If  now  the  sphere  be  approached  to  another  body,  its 
density  will  vary  at  different  parts  of  its  surface,  and  while 
the  charge  is  redistributing  itself  so  as  to  produce  these  differ- 
ences in  density  the  potential  will  vary.  As  soon,  however,  as 
this  redistribution  is  effected  and  no  further  current  exists,  the 
potential  is  the  same  over  all  parts,  though  the  density  differs 
at  different  points. 

Potential,  Electrostatic The  power  of  doing 

work  possessed  by  a  unit  quantity  of  positive  electricity  charged 
on  an  insulated  body. 

The  electric  potential  of  any  point  may  also  be  defined  as 
being  equal  to  the  work  required  to  be  exerted  on  a  unit  of 
positive  electricity  in  bringing  it  to  that  point  from  zero  poten- 
tial, i.  e.,  from  an  infinite  distance. 

Potential  Energy.— Energy  possessing  the  power  or  po- 
tency of  doing  work,  but  not  actually  performing  such  work. 
(See  Energy,  Potential.) 

Potential,  Fall  of (See  Potential,  Electric.) 

Potential,  Magnetic The  amount  of  work  re- 
quired to  bring  up  a  unit  north-seeking  magnetic  pole  from  an 
infinite  distance  to  another  unit  north-seeking  magnetic  pole. 

Potential    of  Conductor,    method*    of  Varying 


490  A  DICTIONARY  OP  ELECTRICAL 


The  potential  of  a  conductor  may  be  varied 

in  the  following  ways  : 

(1)  By  varying  its  electric  charge. 

(2)  By  varying  its  shape  without  altering  its  charge. 

(3)  By  varying  its  position  as  regards  neighboring  bodies. 
This  resembles  the  case  of  a  gas  whose  tension  or  pressure 

may  be  varied  as  follows,  viz. : 

(1)  By  varying  the  quantity  of  gas. 

(2)  By  varying  the  size  of  the  gas  holder  in  which  it  is  kept, 
and, 

(3)  By  varying  the  temperature. 
Difference  of  potential,  therefore  corresponds, 

(1)  With  difference  of  level  in  liquids. 

(2)  With  difference  of  pressure  in  gases. 

(3)  With  difference  of  temperature  in  heat.     (Ayrton.) 
Potential,  Zero An  arbitrary  level  from  which 

electric  potentials  are  measured. 

As  we  measure  the  heights  of  mountains  from  the  arbitrary 
mean  level  of  the  sea  so  we  measure  electric  levels  from  the 
arbitrary  level  of  the  potential  of  the  earth. 

The  true  zero  potential  would  be  situated  at  a  point  infinitely 
distant  from  any  electrified  body. 

Potentiometer.— An  apparatus  for  the  galvanometric 
measurement  of  electro-motive  forces,  or  differences  of  poten- 
tial by  a  zero  method.  (See  Null,  or  Zero  Methods.) 

In  the  potentiometer  the  difference  of  potential  to  be 
measured  is  balanced,  or  opposed,  by  a  known  difference  of 
potential,  and  the  equality  of  the  balance  is  determined  by  the 
failure  of  one  or  more  galvanometers,  placed  in  shunt  circuits, 
to  show  any  movement  of  their  needles. 

The  principle  of  operation  of  the  potentiometer  will  be 
understood  from  an  inspection  of  Fig.  317.  A  secondary  bat- 
tery S,  has  its  terminals  connected  to  the  ends  of  a  uniform 
wire  A  B,  of  high  resistance  called  the  Potentiometer 
Wire.  There  will  therefore  occur  a  regular  drop  or  fall  of 


WORDS,  TERMS  AND  PHRASES.  491 

potential  along-  this  wire,  which,  since  the  wire  is  uniform,  will 
be  equal  per  unit  of  length.  This  drop  of  potential  can  be 
shown  by  connecting  the  terminals  of  a  delicate  high  resis- 
tance galvanometer  to  different  parts  of  the  wire,  when  the 
deflection  of  the  needle  will  be  proportional  to  the  drop  of 
potential  between  the  two  points  of  the  wire  touched.  If 
now  the  terminals  of  a  Standard  Cell  be  inserted  in  the 
circuit  of  the  galvanometer,  so  as  to  oppose  the  current  taken 
from  the  potentiometer  wire,  and  the  contacts  of  the 
potentiometer  wire  be  slid  along  it  until  no  deflection  of 
the  galvanometer  needle  is  produced,  the  drop  of  potential 
between  these  two  points  on  the  potentiometer  wire  will  be 
equal  to  the  difference  of  poten- 
tial of  the  standard  cell.  (See 
Standard  Cell.) 

Suppose  now  it  be  desired  to 
measure  the  difference  of  poten- 
tial between  two  points  a  and  6, 
on  the  wire  C,  through  which  a 
current  is  flowing.  Connect  the 
points  &  and  d,  and  a  and  c,  as  ^' S17' 

shown,  with  the  delicate  high  resistance  galvanometer  G,  in 
either  of  them.  Now  slide  c  towards  d,  until  the  needle  of 
G  shows  no  deflection.  The  potential  between  a  and  b,  is 
then  equal  to  that  between  c  and  d. 

Potentiometer  Wire.— The  wire  of  a  potentiometer 
which  has  been  calibrated  for  its  drop  of  potential.  (See 
Potentiometer.) 

Power.— Rate  of  doing  work. 

Mechanical  power  is  generally  measured  in  horse  power, 
which  is  equal  to  work  done  at  the  rate  of  550  foot-pounds 
per  second. 

The  C.  G.  S.  Unit  of  Power  is  one  Erg  per  Second. 

The  practical  unit  of  power  is  the  Watt,  or  10,000,000  ergs 
per  second. 

1  Watt  =  7±j  H.  P. 


492  A  DICTIONARY  OF  ELECTRICAL 

Power,  Absorptive (See  Absorptive  Power.) 

Power,  Stray (See  Stray  Power.) 

Power,  Thermo-EIectric A  number  which, 

when  multiplied  by  the  difference  of  temperature  of  a  ther- 
mo-electric couple,  will  give  the  difference  of  potential 
thereby  generated  in  micro-volts.  (See  Diagram,  Thermo- 
EIectric.) 

Power,  Units  of Various  units  designed  for  the 

measurement^  power. 

The  following  table  of  UniLs  of  Work,  and  of  Power  is 
taken  from  Hering's  work  on  Dynamo  Electric  Machines  : 
Work 

I  erg  ..f. =1.  dyne-centimetre. 

1     « =  .0000001  joule. 

1  gram-centimetre =  981.00  ergs. 

1  " =  .00001  kilogram-metre. 

1  foot-grain =  1937.5  ergs. 


1  joule,  or 

1  volt-coulomb,    or _. 

1  watt  during  every  sec 


ond,  or. 


1  volt-ampere     during 


every  second 


=  10,000,000  ergs. 


.737324  foot-pound. 


=  .101937  kilogram-metre. 

=  .0013592  metric  horse  power  for 

one  second. 
"  =  .0013406  horse  power  for    one 

second. 

"  =  .0009551  pound-Fah.,  heat  unit 

"  =  .0005306     pound-Centig.,     heat 

unit. 
"  =  .0002407  kilogr.  -  Centig.     heat 

unit. 
=  .0002778  watt-hour. 

1  foot-pound =  13562600  ergs. 

=  1.35626  joules. 


WORDS,  TEEMS  AND    PHRASES.  493 

1  foot-pound =  .13825  kilogram-metre. 

"  =  .0018434  metric  horse-power  for 

one  second. 

"  =.00181818  horse-power  for   one 

second. 

-  =  .0012953  pound-Fah.,  heat  unit, 

=  .0007196  pound  -  Centig.,     heat 

unit. 

=.0003264   kilogr. -Centig.,    heat 

unit. 

=  .0003767  watt-hour. 

1  kilogram-metre =  98100000  ergs. 

=  9.81000  joules. 

=  7.23314  foot-pounds. 

"  =  .01333  metric  horse-power   for 

one  second. 

"  =.013151    horse  -  power    for    one 

second. 

"  =  .009369  pound-Fah. ,  heat  unit. 

"  =  .005205  pound-Centig., heat  unit. 

"  =  .002361  kilogr. -Centig.  heat  unit. 

=  .  002725  watt-hour. 

1  watt-hour =  3600.  joules. 

" =  2654.4  foot-pounds. 

' '         =  366. 97  kilogram-metres. 

=  3.4383  pound-Fah.,  heat  units. 

=  1.9102  pound-Centig.,  heat  units. 

"          =  .8664  kilogr. -Centig.,  heat  units. 

" ...  =  .0013592    metric    horse -power- 
hour. 

=  .0013406  horse-power-hour. 

1  metric  horse-power-hour  =  2648700  joules. 

=  1952940  foot-pounds. 
"  =  270000  kilogram-metres. 

"  =  2529.7  pound-Fah.,  heat  units. 


494  A  DICTIONARY  OF  ELECTRICAL 

1  metric  horse-power-hour  =  1405.4pound-Centig.,  heat  units. 
"  =  637.5  kilogr.-Centig.,  heat  units. 

"  =  735.75  watt-hours. 

"  =  .98634  horse-power-hour. 

1  horse-power-hour =  2685400  joules. 

=  1980000.  foot-pounds. 

"  =  273740  kilogram-metres. 

"  =  2564.8  pound-Fah.,  heat  units. 

"  =  1424.9  pound-Centig.,  heat  units. 

"  t  =  646.31  kilogr.-Centig., heat  units. 

=  745.941  watt-hours. 

=1.01385    metric    horse  -  power  - 

hour. 
Heat. 

1  gram-Centigrade =  .001  kilogram-Centigrade. 

1  pound-Fahrenheit =  1047.03  joules. 

"  =772  foot-pounds. 

"  =  106.731  kilogram-metres. 

"  =  .55556  pound-Centigrade. 

"  =  •  25200  kilogram-Centigrade. 

"  =  .29084  watt-hour. 

"  =.0003953  metric    horse  -  power  - 

hour. 

=  .0003899  horse-power-hour. 

1  pound-Centigrade =  1884.66  joules. 

"  =  1389.6  foot-pounds. 

"  =  192.116  kilogram-metres. 

"  =  1.8000  pound-Fahrenheit. 

"  . .  =  .4536  kilogram-Centigrade. 

"  =  .52352  watt-hour. 

"  =.0007115  metric    horse- power - 

hour. 

"  =  .0007018  horse-power-hour. 

1  kilogram-Centigrade =  4154.95  joules. 

"  =  3063.5  foot-pounds. 


1  kilogram 


WORDS,  TERMS  AND  PHRASES.  495 


Centigrade =  423.54  kilogram-meters. 


=  3.9683  pound-Fahrenheit. 

=  2.2046  pound-Centigrade. 

=  1.1542  watt-hours. 

=.001569    metric    horse- power - 

hour. 
"  =  .0015472  horse-power-hour. 

Power. 

1  erg  per  second =  .0000001  watt. 

1  watt,  or =  10000000.  ergs  per  second. 

1  volt-ampere,  or =  44.2394  foot-pounds  per  min. 

1  joule  per  second,  or =  6.11622    kilogram  -  metres    per 

min. 
1  volt-coulomb  per  second  =  .0573048  Ib.-Fah.,  heat  unit  per 

min. 
"  =  .0318360  Ib.-Cent.,  heat  unit  per 

min. 
"  =  .0144402  klgr.-Cent.    heat   unit 

per  mm. 

"  =  .0013592  metric  horse-power. 

"  =  .0013406  horse-power. 

1  foot-pound  per  min =  226043  ergs  per  second. 

=  .0226043  watt. 

"  =  .13825  kilogram-metre  per  min. 

"  =  .00003072  metric  horse-power. 

=  .000030303  horse-power. 

1  kilogram-metre  per  min  =  1635000.  ergs  per  second. 
"  =  .163500  watt. 

"  =  7.23314  foot-pounds  per  min. 

"  =  .0002222  metric  horse-power. 

"  =  .0002192  horse-power. 

1  metric  horse-power =.  735.75  x  107  ergs  per  second. 

or =  735.750  watts. 

1  French  horse-power =  32549.0  foot-pounds  per  min. 

or =  4500  kilogram-metres  per  min. 


496  A  DICTIONARY  OF  ELECTRICAL 

1  cheval-vapeur,  or =43.162  Ib.-Fah.,  heat  units  per 

min. 

1  force  de  cheval,  or =  23.433  Ib.-Cent.,  heat  units  per 

min. 

1  Pferdekraft =10.625  klg.-Cent.,  heat  units  per 

min. 

"  =  .98634  horse-power  heat    units 

per  min. 

1  horse-power =  745.94  x  107  ergs  per  second. 

"  ..=  745.941  watts. 

"          ' =  33000  foot-pounds  per  min. 

"  =4562.33    kilogram  -  metres    per 

min. 

"  =42.746  Ib.-Fah.,    heat  units  per 

min. 

"  =  23.748  Ib.-Cent,,  heat  units  per 

min. 

"  =  10.772  klg.-Cent.,  heat  units  per 

min. 

"  =  1.01385  metric  horse-power. 

1  Ib.  Fah.,  heat  unit  per 

min =  17.45  x  107  ergs  per  second. 

"  =  17.4505  watts. 

"  =  .23718  metric  horse-power. 

"  =  .023394  horse-power. 

1  Ib.  Cent.,  heat  unit  per 

min =  31.41  x  107  ergs  per  second. 

"  =  31.4109  watts. 

"  =  .04269  metric  horse-power. 

"  =  .042109  horse-power. 

1  klgr. -Cent.,  heat  unit  per 

min =  69.25  x  107  ergs  per  second. 

"  =  69.249  watts. 

"  =  .09412  metric  horse-power. 

"  =  .092835  horse-power. 

(Bering.-) 


WORDS,  TERMS  AND  PHRASES.  497 

Practical  Units.— (See  Units,  Practical.) 
Primary  Battery.— (See  Battery,  Primary.) 

Prime  Conductor. — The  positive  conductor  of  a  fric- 
tional  electric,  or  electrostatic  machine.  (See  Machine,  Elec- 
tric, Frictional.) 

Prime  Motor.— (See  Motor,  Prime.) 

Probe,  Electric Metallic  conductors,  inserted 

in  the  body  of  a  patient,  to  ascertain  the  exact  position  of  a 
bullet  or  other  metallic  body. 

The  conductors  are  placed  parallel,  and  are  separated  at  the 
extremity  of  the  probe  by  any  suitable  insulating  material. 
On  contact  with  the  metallic  substance,  an  electric  bell  is 
rung-  by  the  closing  of  the  circuit,  or  the  same  thing  is  more 
readily  detected  by  the  deflection  of  the  needle  of  a  galvano- 
meter, or  by  a  telephone  placed  in  the  circuit. 

Process,  Electrotype (See  Electrotype  Process.) 

Processes  of  Carbonization. — (See   Carbonization, 

Processes  of.) 
Prony-B rake.— (See  Brake,  Prony.) 

Proof-Plane. — A  small  insulated  conductor  employed  to 
take  test  charges  from  the  surface  of  an  insulated,  charged 
conductor. 

The  proof-plane  is  used  in  connection  with  some  forms  of 
electrometer.— (See  Balance,  Torsion,  Coulomb's.) 

Proof-Plane,  magnetic —A  small 

coil  of  wire  placed  in  the  circuit  of  a  delicate  galvanometer, 
and  used  for  the  purpose  of  exploring  a  magnetic  field. 

When  the  coil  is  suddenly  inverted  in  a  magnetic  field,  if  a 
long  coil  galvanometer  provided  with  a  heavy  needle  is  used, 
the  number  of  lines  of  force  which  pass  through  the  area  of 
cross  section  of  the  coil,  will  be  proportional  to  the  sine  of 
half  the  angle  of  the  first  swing  of  the  needle. 


498  A  DICTIONARY  OF  ELECTRICAL 

Proportionate  Arms  of  ^Electric  Bridge.— A  term 
applied  to  two  of  the  arms  of  an  electric  bridge  or  balance. 
(See  Balance,  Whealstone 's  Electric,  Box  Form  of.) 

Prostration,  Electric (See  Sun  Stroke,  Elec- 
tric.) 

Protection,  Electric of  Houses,  Ships  and 

Buildings  Generally.  (See  Lightning  Rods.) 

Protection,  Electric  of  Metals.— (See 

Metals,  Electric  Protection  of.) 

Protector,  Lightning (See  Lightning  Ar- 
rester.) 

Protector,  Vacuum  Lightning A  protec- 
tor consisting  of  a  glass  vessel  in  which  the  line  wires  and 
an  earth  wire  are  fused,  and  in  which  a  partial  vacuum  is 
maintained. 

Vacuum  protectors  are  employed  on  the  lines  of  submarine 
cables,  or  underground  lines,  in  order  to  protect  them  from 
lightning  discharges. 

A  discharge  of  high  potential  passes  more  readily  through 
this  partial  vacuum  to  the  ground  Lhan  through  the  line 
wires. 

Protoplasm,  Effects  of  Electric  Currents  on 

— Contractions  observed  in  all  protoplasm  on 

the  passage  of  an  electric  current  through  it. 

Protoplasm,  the  basis  of  plant  and  animal  life,  or  the  jelly 
like  matter  that  fills  all  organic  cells,  whatever  may  be  the 
origin  of  such  cells,  suffers  contraction  when  traversed  by  an 
electric  current. 

An  increased  activity  of  the  movements  of  the  amoeba  is 
occasioned  by  slight  shocks  from  an  induction  coil ;  stronger 
discharges  produce  tetanic  contractions,  with,  in  some  cases, 
expulsion  of  food  or  even  of  the  nucleus.  A  uniform 
strength  of  current  produces  contraction  and  imperfect 
tetanus, 


WORDS,  TERMS  AND  PHRASES.  499 

Pump,  mechanical  Air A  mechanical  device 

for  exhausting  or  removing  the  air  from  any  vessel. 

An  excellent  form  of  air  pump  is  shown  in  Fig.  318,  which 
is  a  drawing  of  Bianchi's  pump. 

Three  valves,  all  opening  upwards,  are  placed  at  the  top 
and  bottom  of  the  cylinder,  and  in  the  piston,  respectively. 
These  valves  are  mechanically  opened  and  closed  at  the 
proper  moment  by  the  movements  of  the  piston,  i.  e.,  their 
action  is  automatic.  This  enables 
a  much  higher  vacuum  to  be  ob~ 
tained  than  when  the  valves  open 
and  close  by  the  tension  of  the 
air. 

Mechanical  pumps  are  unable 
to  readily  produce  the  high  vacua 
employed  in  most  electric  lamps. 
Mercury  pumps  are  employed  for 
this  purpose. 

I '  1 1  1 1 1  |  >  • .  mercurial  Air 

Devices  for  obtaining 

high  vacua  by  the  use  of  mercury. 

Mercury  pumps  are,  in  general, 
of  two  types  of  construction,  viz. : 

(1)  The  Geissler  Pump. 

(2)  The  Sprengel  Pump. 

In  the  Geissler  Mercury  Pump, 
Fig.  319,  a  vacuum  is  obtained  by  ' 

means  of  the  Torricellian  vacuum  produced  in  a  large  glass 
bulb  that  forms  the  upper  extremity  of  a  barometric  column. 
(See  Barometric  Column.)  The  lower  end  of  this  tube  or 
column  is  connected  with  a  reservoir  of  mercury  by  means  of 
a  flexible  rubber  tube.  To  fill  the  bulb  with  mercury  the 
reservoir  is  raised  above  its  level,  i.  e.,  above  thirty  inches, 
the  air  it  contains  being  allowed  to  escape  through  an  open- 
ing governed  by  a  stop-cock,  The  vessel  to  be  exhausted  is 


500 


A  DICTIONARY  OF   ELECTRICAL 


Fig.  319, 


\VOKDS,  TERMS   AND   PHRASES. 


501 


connected  with  the  bulb,  and  by  means  of  a  two-way  exhaus- 
tion cock,  communication  can  be  made  with  the  bulb,  when  it 
contains  a  Torricellian 
vacuum,   and  shut  off 
from  it  while  its  air  is 
being  expelled. 

In  actual  practice  the 
mercury  is  mechanic- 
ally pumped  into  the 
barometric  column,  and 
the  valves  are  opened 
either  by  hand,  or,  au- 
tomatically by  suitable 
mechanism,  or  by  elec- 
trical means. 

In  the  Sprengel  Mer- 
cury Pump,  Fig.  320,  a 
vacuum  is  obtained  by 
means  of  the  fall  of  a 
stream  of  mercury  in  a 
vertical  tube  of  compar- 
atively fine  bore,  which 
dips  below  a  mercury 
level.  The  fall  of  a  mer- 
cury stream  causes  the 
exhaustion  of  a  reser- 
voir connected  with  the 
vertical  tube,  by  the  me- 
chanical action  of  the 
mercury  in  entangling 
bubbles  of  air.  These 
bubbles  are  largest  at 
the  beginning  of  the  Fig.  320. 

exhaustion,   but  become  smaller  and  smaller  near  the  end, 
until,  at  last,  the  characteristic  metallic  click  of  mercury  or 


502 


A  DICTIONARY   OF   ELECTRICAL 


other  liquid  falling  in  a  good  vacuum  is  heard.  The  exhaust- 
ion may  be  considered  as  completed  when  the  bubbles  entirely 
disappear  from  the  column. 

The  Sprengel  pump  produces  a  better  vacuum  than  the 
Geissler  pump,  but  is  slower  in  its  action. 

In  actual  practice,  the  mercury  that  has  fallen  through  the 
tube  is  again  raised  to  the  reservoir  connected  to  the  drop  tube 
by  the  action  of  a  mechanical  pump. 

Punning  of  Telegraph  Pole§.— Ramming  or  packing 
the  earth  around  the  base  of  a  telegraph 
pole  for  the  purpose  of  more  securely 
fixing  it  in  the  ground. 

Push  Button.— (See  Button,  Push.) 

Pyro  Electricity. — Electricity  de- 
veloped in  certain  crystalline  bodies  by 
heating  or  cooling  them. 

Tourmaline  possesses  this  property  in 
a  marked  degree.  When  a  crystal  of 
tourmaline  is  heated  or  cooled,  it  acquires 
opposite  electrifications  at  opposite  ends 
or  poles. 

In  the  crystal  of  tourmaline  shown  in 
Fig.  321,  the  end  A,  called  the  analogous 
pole,  acquires  a  positive  electrification,  and  the  end  B,  called 
the  antilogous  pole,  a  negative  electrification,  while  the  tem- 
perature of  the  crystal  is  rising.  While  cooling  the  opposite 
electrifications  are  produced. 

A  heated  crystal  of  tourmaline,  suspended  by  a  fibre,  is  at- 
tracted or  repelled  by  an  electrified  body  or  by  a  second  heated 
tourmaline,  in  the  same  manner  as  an  electrified  body. 

Many  crystalline  bodies  possess  similar  properties.  Among 
these  are  the  ore  of  zinc  known  as  electric  calamine  or  the 
silicate  of  zinc,  boracite,  quartz,  tartrate  of  potash,  sulphate 
of  quinine,  etc. 


A 

Fig.  321. 


WORDS,  TERMS  AND  PHRASES. 


503 


Pyromaglietic  Motor.— A  motor  driven  by  the  attract 
tion  of  magnet  poles  on  a  movable  core  of  iron  unequally 
heated. 


Fig.  sea, 

The  intensity  of  magnetization  of  iron  decreases  with  an  in- 
crease of  temperature,  iron  losing  most  of  its  magnetization  at 


A  DICTIONARY  OF   ELECTRICAL 


a  red  heat.  A  disc  of  iron,  placed  between  the  poles  of  a 
magnet  so  as  to  be  capable  of  rotation,  will  rotate  if  heated 
at  a  part  nearer  one  pole  than  the  other,  since  it  becomes  less 
powerfully  magnetized  at  the  heated  part 


Fig.  323. 

In  the  form  of  pyromagnetic  motor  devised  by  Edison,  and 
shown  in  Fig.  322,  in  elevation,  and  in  Fig.  323,  in  vertical  sec- 


WORDS,  TERMS  AND  PHRASES. 


505 


tion,  the  disc  of  iron  is  replaced  by  a  series  of  small  iron  tubes, 
or  divided  annular 
spaces,  heated  by  the 
products  of  combustion 
from  a  fire  placed  be- 
neath them.  In  order 
to  render  this  heating 
local,  a  flat  screen  is 
placed  dissymetrically 
across  the  top  to  pre- 
vent the  passage  of  air 
through  the  portion  of 
the  iron  tubes  so 
screened.  The  air  is 
supplied  to  the  furnace 
by  passing  down  from 
above  through  the  tubes 
so  screened.  This  is 
shown  in  the  drawings, 
the  direction  of  the 
heating  and  the  cooling 
air  currents  being  in- 
dicated by  the  arrows. 
The  supply  of  air  from 
above  thus  insures  the 
more  rapid  cooling  of 
the  screened  portion  of 
the  tubes. 

I»yro  magnetic 
Generator  or  Dy- 
lianio. — An  apparatus 
for  producing  electric- 
ity directly  from  the 
burning  of  fuel.  Flg.stU. 

The  operation  of  the  generator  is  dependent  on  the  fact, 


506  A  DICTIONARY  OF  ELECTRICAL 

that  any  variation  in  the  number  of  lines  of  magnetic  force 
that  pass  through  a  conductor,  will  develop  differences  of 
electric  potential  therein.  Such  variations  may  be  effected 
either  by  varying  the  position  of  the  conductor  as  regards 
the  magnetic  field,  or  by  varying  the  intensity  of  the  magnetic 
field  itself.  The  latter  method  of  generating  differences  of 
potential  is  utilized  in  the  pyromagnetic  generator,  and  is 
effected  in  it  by  varying  the  magnetization  of  rolls  of  thin 
iron  by  the  action  of  heat. 

A  form  of.  pyromagnetic  generator  devised  by  Edison  is 
shown  in  Figs.  324  and  325. 

Eight  electro-magnets  are  provided  each  with  an  armature, 
consisting  of  a  roll  of  corrugated  iron.  Each  of  these  arma- 
tures is  provided  with  a  coil  of  insulated  wire  wound  on  it 
and  protected  by  asbestos  paper.  These  armatures  pass 
through  two  iron  discs  as  shown.  The  armature  coils  are  con- 
nected in  series  in  closed  circuit,  the  wires  from  the  coils  being 
connected  with  metallic  brushes  that  rest  on  a  commutator, 
supported  on  a  vertical  axis.  A  pair  of  metallic  rings  is 
provided  above  the  commutator  to  carry  off  the  current  gene- 
rated. The  vertical  axis  is  provided  below  with  a  semi- 
circular screen  called  a  guard  plate  which  rotates  with  the 
axis  and  cuts  off  or  screens  one-half  the  iron  armatures  from 
the  heated  air. 

When  the  axis  is  rotated,  the  differences  in  the  magnetiza- 
tion of  the  armatures,  when  hot  and  cold,  develop  differences 
in  electromotive  force  which  result  in  the  production  of  an 
electric  current. 

Pyrometer. — An  instrument  for  determining  tempera- 
tures higher  than  those  that  can  be  readily  measured  by  ther- 
mometers. 

Pyrometers  are  operated  in  a  variety  of  ways.  A  common 
method  is  by  the  expansion  of  a  metal  rod. 

Pyrometer,  Siemens'  Electric An 


WORDS,  TERMS   AND  PHRASES.  507 

apparatus  for  the  determination  of  temperature  by  the  meas- 
urement of  the  electric  resistance  of  a  platinum  wire  exposed 
to  the  heat  whose  temperature  is  to  be  measured. 


Fig.  $25. 

The  platinum  wire  is  coiled  on  a  cylinder  of  fire-clay,  so 
that  its  separate  convolutions  do  not  touch  one  another.  It  is 
protected  by  a  platinum  shield,  and  is  exposed  to  the  tempera- 
ture to  be  measured  while  inside  a  platinum  tube. 

The  resistance  of  the  platinum  coil  at  0°  C.  having  been 


50«  A  DICTIONARY  OF  ELECTRICAL 

accurately  ascertained,  the  temperature  to  which  it  has  been 
exposed  .can  be  calculated  from  the  change  in  its  resistance 
when  exposed  to  the  unknown  temperature. 

Pyrometer,  Siemens'  Water —A  pyrometer 

employed  for  determining-  the  temperature  of  a  furnace,  or 
other  intense  source  of  heat,  by  calorimetric  methods,  i.  e.,  by 
the  increase  in  the  temperature  of  a  known  weight  of  water, 
into  which  a  metal  cylinder  of  a  given  weight  has  been  put, 
after  being  exposed  for  a  given  time  to  the  source  of  heat 
to  be  measured. 

When  copper  cylinders  are  employed,  the  instrument  pos- 
sesses a  range  of  temperature  of  1800°  F.;  when  a  platinum 
cylinder  is  used,  it  has  a  range  of  2700°  F. 

quadrant  Electroscope,   Henley's (See 

Electroscope,  Quadrant,  Henley's.) 

Quadrant  Electrometer.— (See  Electrometer,  Quad- 
rant.) 

Quadruples  Telegraphy.— A  system  of  telegraphy  by 
means  of  which  four  messages  can  be  simultaneously  trans- 
mitted over  a  single  wire,  two  in  one  direction,  and  two  in  the 
opposite  direction. — (See  Telegraphy,  Quadruplex.) 

Qualitative  Analysis.— (See  Analysis.) 

Quality  of  Disruptive  Discharge,  How  Affected. 

— The  appearance  of  the  disruptive  discharge  as  affected  by  a 
variety  of  circumstances.— (See  Discharge,  Disruptive.) 

Quality  or  Timbre  of  §ound.— That  peculiarity  of  a 
musical  note  which  enables  us  to  distinguish  it  from  another 
musical  note  of  the  same  tone  or  pitch,  and  of  the  same  in- 
tensity or  loudness,  but  sounded  on  another  instrument. 

The  middle  C,  for  example  of  a  pianoforte,  is  readily  dis- 
tinguishable from  the  same  note  on  a  flute,  or  on  a  violin  ;  that 
is  to  say,  its  quality  is  different.  The  differences  in  the  quality 
of  musical  sounds  are  caused  by  the  admixture  of  additional 


WORDS,  TEEMS  AND  PHRASES.  509 

sounds  called  overtones  which  are  always  associated  with  any 
musical  sound. 

Briefly,  nearly  all  so-called  simple  musical  sounds,  are  in 
reality  chords  or  assemblages  of  a  number  of  different  musical 
sounds. 

One  of  these  notes  is  far  louder  than  all  the  others  and  is 
called  the  fundamental  tone  or  note,  and  is  what  is  recognized 
by  the  ear  as  the  note  proper.  The  overtones  are  too  feeble 
to  be  heard  very  distinctly,  but  their  presence  gives  to  the  note 
proper  its  own  peculiar  quality.  In  the  case  of  a  note  sounded 
on  the  flute,  these  overtones  are  different  either  in  number 
or  in  their  relative  intensities  from  the  same  note  sounded  on 
another  instrument.  Their  fundamental  tones,  however,  are 
the  same. 

The  peculiarities  which  enable  us  to  distinguish  the  voice 
of  one  speaker  or  singer  from  another  are  due  to  the  presence 
of  these  overtones.  The  over-tones  must  be  correctly  repro- 
duced by  the  diaphragm  of  the  telephone,  or  phonograph, 
graphophone,  or  gramophone,  if  the  articulate  speech  is  to  be 
correctly  reproduced  with  all  its  characteristic  peculiarities. 

Quantitative  Analysis.— (See  Analysis.) 

Quantity,  Arrangement  of  Voltaic  Cells  for 

— A  term,  now  generally  in  disuse,  to  indicate  the  grouping  of 
voltaic  cells,  technically  known  as  parallel  or  multiple-arc. 

The  arrangement  or  coupling  of  a  number  of  voltaic  cells 
in  multiple-arc  being  an  arrangement  that  reduces  the  internal 
resistance  of  the  battery,  and  thus  permits  a  greater  current, 
or  quantity  of  electricity  to  pass  ;  hence  the  origin  of  the  term. 

Quantity,  Unit  of  Electric A  definite  amount 

or  quantity  of  electricity  called  the  coulomb. — (See  Coulomb.) 

Although  the  exact  nature  of  electricity  is  unknown,  yet 
it  acts  like  a  fluid  (a  liquid  or  gas)  and  can  be  accurately 
measured  as  to  quantity. 

A  current  of  one  ampere,  for  example,  is  a  current  in  which 
one  coulomb  of  electricity  passes  in  every  secon-1. 


510  A  DICTIONARY  OF  ELECTRICAL 

A  condenser  of  the  capacity  of  one  farad  is  large  enough 
to  hold  one  coulomb  of  electricity  if  forced  into  the  vessel 
under  an  electro-motive  force  of  one  volt.—  (See  Capacity. 
Farad.  Volt.) 

Quiet  Discharge. — (See  Discharge,  Convective.) 

Radiant  Energy.— Energy  transferred  to,  or  charged  on, 
the  universal  ether. 
Radiant  energy  is  of  two  forms,  viz.  : 

(1)  Obscure  Radiation,  or  Heat. 

(2)  Lumiribus  Radiation,  or  Light. 

Radiant  Matter.— (See  Matter,  Radiant.) 

Radiophony.— The  production  of  sound  by  a  body  cap- 
able of  absorbing  radiant  energy,  when  an  intermittent  beam 
of  light  or  heat  falls  on  it. 

The  action  of  radiant  energy,  when  absorbed  by  matter,  is 
to  cause  its  expansion  by  the  consequent  increase  of  temper- 
ature. This  occurs  even  when  the  body  is  but  momentarily 
exposed  to  a  flash  of  light,  but  the  instantaneous  expansion, 
thus  produced,  immediately  dies  away,  and  by  itself  is  indis- 
tinguishable. If,  however,  a  sufficiently  rapid  succession  of 
such  flashes  fall  on  the  body,  the  instantaneous  expansions 
and  contractions  produce  an  appreciable  musical  note. 

The  sounds  so  produced  have  been  utilized  by  Bell  and 
Tainter  in  the  construction  of  the  Photophone.  (See  Photo- 
phone.) 

Radiation.— The  transference  of  energy  by  means  of 
ether  waves. 

Radicals.— Unsaturated  atoms  or  molecules,  in  which 
one  or  more  of  the  bonds  are  left  open  or  free. 

Radicals  are  either  Simple  or  Compound. 

The  radical  may  be  regarded  as  the  basis  to  which  other 
elements  may  be  added,  or  as  the  nucleus  around  which  they 
may  be  grouped. 


WORDS,  TEEMS  AND  PHRASES.  511 

Thus  HaO  forms  a  complete  chemical  molecule,  because 
the  bonds  of  all  its  constituent  atoms  are  saturated,  thus 
H  —  O  —  H.  But  H  —  O  — ,  or  hydroxyl,  is  a  radical,  because 
its  oxygen  atom  possesses  one  unsaturated  or  free  bond.  By 
combining  with  the  radical,  (NO8),  it  forms  nitric  acid,  thus 
H  —  O  —  (NO,)  =  HN08. 

During  electrolysis,  the  molecule  of  the  electrolyte  is  de- 
composed into  two  simple  or  compound  radicals,  called  ions. 
These  ions  are  respectively  electro-positive  or  electro-negative, 
and  are  called  Jcathions  and  anions.  (See  Ions.  Electrolysis.) 

Radiometer,  Crookes' An  apparatus  for 

showing  the  action  of  radiant  matter  in  producing  motion 
from  the  effect  of  the  reaction  of  a  stream  of  molecules  escap- 
ing from  a  number  of  easily  moved  heated  surfaces.  (See 
Matter,  Radiant.) 

Rail  Road,  or  Railway,  Electric A  rail- 
road, or  railway,  the  cars  on  which  are  driven  or  propelled 
by  means  of  electric  motors  connected  with  the  cars. 

The  electric  current  that  drives  the  electric  motor  is  either 
derived  from  storage  batteries  placed  on  the  cars,  or  from 
a  dynamo-electric  machine  or  battery  of  dynamo-electric 
machines,  conveniently  situated  at  some  point  on  the  road. 
(See  Storage  of  Electricity.)  The  current  from  the  dynamo  is  led 
along  the  line  by  suitable  electric  conductors.  This  current  is 
passed  into  the  electric  motor  as  the  car  runs  along  the 
tracks,  in  various  ways,  viz.: 

(1)  Placing  one  or  both  rails  in  the  circuit  of  the  dynamo  and 
taking  the  current  from  the  tracks  by  means  of  sliding  or 
rolling  contacts  connected  with  the  motor. 

(2)  By  placing  the  conducting  wires  parallel  to  each  other 
in  a  longitudinally  slotted  underground  conduit  in  the  road 
bed,  and  taking  the  current  by  means  of  a  traveling  brush  or 
roller,  called  a  plow,  sled  or  shoe,  and  provided  with  two  cen- 
tral plates,  insulated  from  one  another  and  connected  re- 
spectively to  the  motor  terminals.    On  the  movement  of  the 


512  A  DICTIONARY  OF  ELECTRICAL 

car  over  the  track,  these  traveling  contacts  touch  the  two 
parallel  line  conductors  in  the  conduit,  and  take  the  electric 
current  therefrom.  (See  Plow,  Sled.} 

(3)  By  placing  the  line  conductors  on  poles,  along  the  road, 
and  taking  the  current  therefrom  by  means  of  suitable  travel- 
ing contacts  called  trolleys  or  by  sliders.  (See  Trolleys.) 

The  first  method,  viz.,  that  of  using  the  tracks  alone  as  con- 
ductors is  not  much  employed. 

The  use  of  the  track  and  ground  as  a  return  for  the  current 
is  now  very  generally  employed. 

In  some  systems  the  track  is  divided  into  sections  which  are 
successively  brought  into  action  with  the  main  conductors  by 
contacts  effected  by  the  attraction  between  magnets  carried 
on  the  car  and  contact  pieces  of  magnetic  material  placed  be- 
low the  surface.  The  rail  section  thus  temporarily  energized 
is  placed  in  connection  with  the  motor. 

In  order  to  regulate  the  speed,  various  devices  are  employed 
to  vary  the  current  strength  in  the  motor  circuit.  These 
devices  consist  essentially  in  rheostats  or  resistances  intro- 
duced into,  or  removed  from,  the  motor  circuit  by  the  move- 
ment by  hand  of  a  lever  that  forms  part  of  the  circuit,  over 
contact  plates  connected  to  the  resistance  coils. 

In  order  to  change  the  direction  of  the  car,  the  direction  of 
rotation  of  the  electric  motor  is  changed.  This  is  effected  by 
some  form  of  reversing  gear  or  mechanism  that  changes  the 
direction  of  rotation  of  the  motor,  either  by  shifting  the 
brushes,  by  changing  the  field,  or  by  any  other  means.  (See 
Telpherage.  Electric  Motor.  Rheostat.) 

Ray,  Electric (See  Fishes,  Electric.) 

Rays,  Actinic (See  Antinic  Rays.) 

Reaction  Principle  of  Dynamo-Electric  Ha- 
chines. — The  reaction  of  the  field  magnets  and  the  armature 
of  a  dynamo-electric  machine  on  each  other  until  the  full  work- 
ing current  which  the  machine  is  capable  of  developing  is  pro- 
duced, 


WOKDS,  TERMS  AND  PHRASES.  513 

When  the  armature  of  a  series  or  shunt  dynamo  commences 
to  rotate,  the  differences  of  potential  generated  in  its  coils  are 
very  small,  since  the  field  of  the  magnet  is  so  weak.  The  cur- 
rent so  produced  in  the  armature,  however, circulating  through 
the  field  magnet  coils,  increases  the  intensity  of  the  mag- 
netic field  of  the  machine,  and  this  reacting  on  the  arma- 
ture results  in  a  more  powerful  current  through  it.  This  cur- 
rent again  increases  the  strength  of  the  magnetic  field  of  the 
machine,  which  again  reacts  to  increase  the  current  strength 
of  the  armature  coils,  and  this  continues  nntil  the  machine 
is  producing  the  full  current  it  is  designed  to  produce. 

A  dynamo-electric  machine  very  rapidly  "  builds  up,"  or 
reaches  its  maximum  current  after  starting.  The  reaction 
principle  was  discovered  by  Soren  Hjorth,  of  Copenhagen. 

Reaction  Telephone.— An  electro-magnetic  telephone 
in  which  the  currents  induced  in  a  coil  of  wire  attached  to 
the  diaphragm  are  passed  through  the  coils  of  the  electro- 
magnet and  thus  react  on  and  strengthen  it. 

Rcaetion  Wheel,  Electric (See  Flyer, 

Electric.) 

Reactions,  Anodic  and  Kathodic (See  Kath- 

odic  and  Anodic  Reactions.) 

Reading  Telescope.— (See  Telescope,  Reading.) 

Receiver,  Harmonic  —  —A  receiver,  employed 

in  systems  of  harmonic  telegraphy,  containing  an  electro- 
magnetic reed,  tuned  to  vibrate  to  one  note  or  tone  only.  (See 
Telegraphy,  Harmonic.) 

Receiver,  Phonographic,  Telephonic,  Grapho- 

phonic,  Gramophonic The  apparatus  employed 

in  a  telephone,  phonograph,  graphophone,  or  gramophone, 
for  the  reproduction  of  articulate  speech.  (See  Phonograph.) 

Reciprocals. — The  quotient  arising  from  dividing  unity 
by  any  number. 

The  reciprocal  of  4  is  ^  or  .250. 


514 


A  DICTIONARY  OF  ELECTRICAL 


The  conducting  power  of  any  circuit  is  equal  to  the  re- 
ciprocal of  its  resistance,  or,  in  other  words,  the  conducting 
power  is  inversely  proportional  to  the  resistance. 

The  following  table  contains  the  reciprocals  of  the  numerals 
up  to  100 : 

Table  of  Reciprocals. 


No. 

Recip- 
rocal. 

No. 

Recip- 
rocal. 

No. 

Recip- 
rocal. 

No. 

Recip- 
rocal. 

No. 

Recip- 
rocal. 

2 

0.5000 

'22 

0.0455 

42 

0.0338 

62 

0.0161 

82 

0.0122 

3 

0.3333 

23 

0.0435 

43 

0.0233 

63 

0.0159 

83 

0.0120 

4 

0.2500 

24 

0.0417 

44 

0.0227 

64 

0.0156 

84 

0.0119 

5 

0.2000 

25 

0.0400 

45 

0.0222 

65 

0.0154 

85 

0.0118 

6 

0.1667 

26 

0.0385 

46 

0.0217 

66 

0.0152 

86 

0.0116 

7 

0.1429 

27 

0.0370 

47 

0.0213 

67 

0.0149 

87 

0.0115 

8 

0.1250 

28 

0.0357 

48 

0.0208 

68 

0.0147 

88 

0.0114 

9 

0.1111 

29 

0.0345 

49 

0.0204 

69 

0.0145 

89 

0.0112 

10 

0.1000 

30 

0.0333 

50 

0.0200 

70 

0.0143 

90 

0.0111 

11 

0.0909 

31 

0.0323 

51 

0.0196 

71 

0.0141 

91 

0.0110 

12 

0.0833 

32 

0.0313 

52 

0.0192 

72 

0.0139 

92 

0.0109 

13 

0.0769 

33 

0.0303 

53 

0.0189 

73 

0.0137 

93 

0.0108 

14 

0.0714 

34 

0.0294 

54 

0.0185 

74 

0.0135 

94 

0.0106 

15 

0.0667 

35 

0.0286 

55 

0.0182 

75 

0.0133 

95 

0.0105 

16 

0.0625 

36 

0.0278 

56 

0.0179 

76 

0.0132 

96 

0.0104 

17 

0.0588 

37 

0.0270 

57 

0.0175 

77 

0.0130 

97 

0.0103 

18 

0.0556 

38 

0.0263 

58 

0.0172 

78 

0.0128 

98 

0.0102 

19 

0.0526 

39 

0.0256 

59 

0.0169 

79 

0.0127 

99 

0.0101 

20 

0.0500 

40 

0.0250 

60 

0.0167 

80 

0.0125 

100 

0.0100 

21 

0.0476 

41 

0.0244 

61 

0.0164 

81 

0.0123 

(Clark  &  Sabine.) 

Record,  Gramophonic,  Graphophonic,  or  Phon- 
ographic   The  irregular  indentations,  cuttings,  or 

tracings  made  by  a  point  attached  to  the  diaphragm  spoken 
against,  and  employed  in  connection  with  the  receiving 
diaphragm  for  the  reproduction  of  articulate  speech. 

Record,  Telephonic A  permanent  record  pro- 
duced by  the  diaphragm  of  a  telephone. 


WOUDS,  TERMS  AND  PHRASES. 


515 


Various  methods  have  been  proposed  for  telephone  records, 
but  none  of  them  have  yet  been  introduced  into  actual  com- 
mercial use. 


Recorder,  Bain's  Chemical 


— An  apparatus 


for  recording  the  dots  and  dashes  of  a  Morse  telegraphic 
dispatch,  on  a  sheet  of  chemically  prepared  paper. 

A  fillet  of  paper  soaked  in  some  chemical  substance,  such 
as  ferro-cyanide  of  potassium,  is  moved  at  a  uniform  rate 
between  the  two  terminals  of  the  line,  one  of  which  is  iron 
tipped,  so  that  on  the  passage  of  the  current,  a  blue  dot,  or 
dash,  will  be  made  on  the  paper  according  to  the  length  of 
time  the  current  is  passing. 

In  order  to  ensure  a  moist  condition  of  the  paper  fillet  some 
deliquescent  salt,  like 
ammonium  nitrate,  is 
generally  mixed  with  the 
ferro-cyanide  of  potas- 
sium. 

A  Bain  Recorder  is 
shown  in  Fig.  326.  A,  is 
a  drum  of  brass,  tinned 
on  the  outside.  The 
paper  fillet  is  drawn 
from  the  roll  and  kept  pressed  against  the  cylinder  A,  by  a 
small  wooden  roller  B.  The  needle,  which  is  a  metallic  point, 
is  in  connection  with  one  end  of  the  line  wire,  and  the  brass 
drum  is  connected  with  the  other  end  through  the  earth. 
Care  must  be  observed  to  connect  the  needle  point  with  the 
positive  electrode,  as  otherwise  the  paper  will  not  be  marked. 

The  Bain  Recorder  is  now  almost  entirely  replaced  by  the 
Morse  Sounder. 


Recorder,   Worse 


or  Morse    Register.— An 


apparatus  for  automatically  recording  the  dots  and  dasltes  of 
a  Morse  telegraphic  dispatch,   on  a  fillet  of  paper    drawn 


516 


A  DICTIONARY   OF  ELECTRICAL 


under  an  indenting  or  marking  point  on  a  striking  lever,  con- 
nected with  the  armature  of  an  electro-magnet. 

The  Morse  registering  or  recording  apparatus  is  shown  in 
Fig.  327. 

The  paper  fillet  passes  between  a  pair  of  rollers  r.  driven 
by  the  clockwork  W.  The  upper  roller  is  provided  with  a 
groove,  so  that  the  depi'ession  of  the  stylus  at  the  bent  end 
of  the  lever  L,  by  the  electro-magnet  M,  moving  its  arma- 
ture attached  to  the  lever  L,  may  indent  or  emboss  the  paper 
fillet.  When  no  current  is  passing,  the  armature  of  the 
magnet  and  the  lever  L,  are  drawn  back  by  the  action  of  an 
adjustable  spring  at  n. 


In  the  drawing,  the  ordinary  Morse  sounder  is  shown  on  the 
right.  The  sounder  has  almost  entirely  replaced  the  record- 
ing apparatus. 

Recorder,  Siphon —  An  apparatus  for  re- 
cording in  ink  on  a  sheet  of  paper,  by  means  of  a  fine  glass 
siphon  supported  on  a  fine  wire,  the  message  received  over  a 
cable. 

One  end  of  the  siphon  dips  in  a  vessel  of  ink.  The  record  is 
received  on  a  fillet  of  paper  moved  mechanically  under  the 
siphon.  The  ink  is  discharged  from  the  siphon  by  electric 
charges  imparted  to  the  ink  by  a  static  electric  machine. 


WORDS,  TERMS   AND  PHRASES. 


517 


In  the  annexed  sketch  of  the  siphon  recorder,  Fig.  328,  a  light 
rectangular  coil  6  b,  of  very  fine  wire,  is  suspended  by  a 
fine  wire//',  between  the  poles  N,  S,  of  a  powerful  com- 
pound permanent  magnet,  and  moving  on  the  vertical  axis 
of  the  supporting  wire//',  adjustable  as  to  tension,  at  h. 
A  stationary  soft  iron  core  a,  is  magnetized  by  induction 


fig.  328. 

and  strengthens  the  magnetic  field  of  N,  S.  The  cable  cur- 
rent is  received  by  the  coil  b  b,  through  the  suspending  wire 
//',  and  is  moved  by  it  to  the  right  or  the  left,  according 
to  its  direction,  to  an  extent  that  depends  on  the  current 
strength. 

The  fine  glass  siphon  n,  which  dips  into  a  reservoir  of  ink  at 
TO,  is  capable  of  movement  on  a  vertical  axis  I,  and  is  moved 
backwards  or  forwards,  in  one  direction  by  a  thread  fc, 


518  A  DICTIONARY  OF  ELECTRIC  At1 

attached  to  6,  and  in  the  opposite  direction  by  a  retractile 
spring  attached  to  an  arm  of  the  axis  /. 

As  the  paper  is  moved  under  the  point  of  the  siphon,  an 
irregular  curved  line  is  marked  thereon. 

Two  records  as  actually  received  by  a  siphon  recorder  are 
shown  in  the  Figs.  329  and  330.     Movements  upwards  corre- 
spond to  the  dots,  and  downwards  to  dashes. 
Rectilinear  Currents.    (See  Currents,  Rectilinear.) 
Reflecting   Galvanometer.— (See   Galvanometer,  Re- 
flecting.) 

Reflector,    Parabolic (See  Parabolic  Re- 
flector.) 

Reflectors.— 
Plane  or  curved  sur- 
faces capable  of  regu- 
larly 


SIPHON   RECORDER 

Fig- 329'  flectors.) 

Refraction,  Double The  property  possessed 

by  certain  bodies  of  splitting  up  by  refraction  a  ray  of  light 
passed  into  it,  into  two  separate  /*v  — 

rays,   and  thus   doubly  refract-  »«*^*(/~v*~^\/r**<~- 

Certain  specimens  of  calc  spar 

possess  the  property  of  double  refraction.     Each  of  the  two 
rays  into  which  the  original  ray  is  separated  is  polarized. 

Refraction,  Double  Electric The  prop- 
erty of  doubly  refracting  light  acquired  by  some  transparent 
substances  when  placed  in  an  electrostatic  or  electro-magnetic 
field.  (See  Double  Refraction,  Electric.) 

Register,  Watchman's  Electric (See  Watch- 
man's Register,  Electric.) 

Registering  Apparatus,  Electric    -  —De- 

vices for  obtaining  permanent  records  by  electrical  means. 
(See  Recorders.) 


WORDS,  TERMS  AND  PHRASES. 


519 


Regulation,  Automatic  -  —  —(See  Automatic 
Regulation.) 

Relative  Calibration.— (See  Calibration,  Absolute  and 
Relative.) 

Relay  Bell.— (See Bell,  Relay.) 

Relay,  microphone (See  Microphone  Relay.) 

Relay,  or  Receiving  Magnet.— An  electro-magnet 
employed  in  systems  of  telegraphy  provided  with  contact- 
points,  placed  on  a  delicately  supported  armature,  the  move- 
ments of  which  throw  a  battery,  called  the  local  battery,  into 
or  out  of  circuit,  for  the  operation  of  the  recording  apparatus. 


Fig.  331. 

The  use  of  a  relay  permits  much  smaller  currents  to  be 
used  than  could  otherwise  be  done,  since  the  electric  impulses, 
on  reaching  a  distant  station,  are  required  to  do  no  other  work 
than  attracting  a  delicately  poised  movable  contact,  and  thus, 
by  throwing  a  local  battery  into  the  circuit  of  the  receiving 
apparatus,  to  cause  such  local  battery  to  perform  the  work  of 


520  A   DICTIONARY   OF   ELECTRICAL 

registering.  Its  use  is  especially  required  in  the  Morse  system 
of  telegraphy  in  order  to  cause  the  Sounder  to  be  distinctly 
heard. 

A  form  of  relay  much  used  is  shown  in  Fig.  831. 

The  electro-magnet  M,  is  wound  with  many  turns  of  very 
fine  wire.  In  the  form  used  by  the  Western  Union  Telegraph 
Company,  there  are  about  8,500  turns,  having  resistance  of 
150  ohms.  A  screw  m,  is  provided  for  moving  the  electro- 
magnet M,  a  slight  distance  in  or  out  for  the  purposes  of  ad- 
justment. A  semi-cylindrical  armature  A,  of  soft  iron,  is 
attached  to  the  insulated  armature  lever  a,  the  lower  end  of 
which  is  supported  by  a  steel  arbor,  which  is  pivoted  between 
two  set  screws.  A  retractile  spring  S',  regulable  at  S,  is  pro- 
vided for  moving  the  armature  away  from  the  electro-magnet. 
There  are  four  binding  posts,  two  of  which  are  placed  in  the 
circuit  of  the  electro-magnet,  and  two  in  that  of  the  local 
battery.  The  ends  of  the  line  wire  are  connected  with  the 
former,  and  the  receiving  instrument  placed  in  the  circuit  of 
the  latter.  A  platinum  contact  is  placed  on  the  end  of  a  screw 
supported  at  F,  opposite  a  similar  contact,  near  the  end  a,  of 
the  armature  lever.  The  contact  is  regulable  by  means  of 
a  screw  c. 

On  the  the  energizing  of  the  electro-magnet,  the  attraction 
of  its  armature  closes  the  platinum  contact,  and  by  thus  com- 
pleting the  circuit  of  the  local  battery  causes  an  attraction  of 
the  armature  of  the  receiving  apparatus.  On  the  cessation  of 
the  current  in  the  main  line,  the  spring-  S',  pulls  the  armature 
away  from  the  magnet,  breaks  the  current  of  the  local  battery, 
and  thus  permits  a  similar  spring  on  the  receiving  instrument 
to  pull  its  armature  away.  Thus  all  the  movements  of  the 
armature  of  the  relay  are  reproduced  with  increased  intensity 
by  the  armature  of  the  receiving  instrument. 

The  connections  of  the  relay  to  the  local  battery  and  the 
registering  apparatus,  will  be  better  undei-stood  from  an  in- 
spection of  Fig.  332,  which  represents  a  form  of  relay  much 


WORDS,  TERMS  AND  PHRASES.  521 

used  in  Germany.  The  retractile  spring  /,  is  regulated  by 
the  up-and-down  movements  of  its  lower  support,  which  slides 
in  the  vertical  pillar  S.  The  line  wire  is  shown  at  m  m,  con- 
nected at  one  end  to  earth  by  the  ground  wire.  The  register- 
ing apparatus,  R,  is  connected  in  the  circuit  of  the  local  bat- 
tery L,  as  shown.  The  contacts  are  made  by  the  end  B, 
of  the  lever  B  B',  attached  to  the  armature  A,  of  the  electro- 
magnet M  M. 

JD 


Fig.  SSS. 

Relay,  Polarized  —  — A  telegraphic  relay  provided 
with  a  permanently  magnetized  armature  in  place  of  the  soft 
iron  armature  of  the  ordinary  instrument. 

In  the  form  of  polarized  relay  shown  in  Fig.  333,  N  S,  is  a 
steel  'magnet,  whose  magnetism  is  consequently  permanent, 
with  its  north  and  south  poles  at  N  and  S,  respectively.  The 
cores  of  the  electro-magnet  m  m',  are  of  soft  iron,  and,  since 
they  rest-on  the  north  pole  N  of  the  permanent  steel  magnet 


522  A   DICTIONARY  OF  ELECTRICAL 

the  poles,  brought  very  near  together  by  the  armatures  at 
n,  ri,  will  be  of  the  same  polarity  as  N,  when  no  current  is 
passing  through  the  coils  m,  m' ;  but  when  such  current  does 
pass,  one  of  these  poles  becomes  of  stronger  north  polarity, 
while  the  other  changes  its  polarity  to  south.  By  this  means 
to-and-fro  movements  of  the  armature  lever  with  its  contact 
point  are  effected  without  the  use  of  a  retractile  spring ; 
movement  in  one  direction  occurring  on  the  closing  of  the 
circuit  through  the  electro-magnetism  developed  by  the  coils 


Fig.  333. 

m,  m',  and  movement  in  the  opposite  direction,  on  the  losing 
of  this  magnetism  on  breaking  the  circuit,  by  the  permanent 
magnetism  of  the  steel  magnet  N  S.  These  movements  are 
imparted  to  the  soft  iron  lever  c  c',  pivoted  at  B,  and  passing 
between  the  closely  approached  soft  iron  poles  at  n,  n'.  This 
lever  rests  at  the  end  c'  against  a  contact  point  when  moved 
in  one  direction,  and  against  an  insulated  point  when  moved 
in  the  opposite  direction.  It  rests  against  the  insulated  point 
when  no  current  is  passing  through  the  coils  m,  m'. 
If  the  armature  lever  were  placed  in  a  position  exactly  mid- 


WORDS,  TERMS  AND  PHRASES.  523 

way  between  the  poles  n  and  ri,  it  would  not  move  at  all, 
being  equally  attracted  by  each  ;  but  if  moved  a  little  nearer 
one  pole  than  the  other,  it  would  be  attracted  to,  and  rest 
against,  the  nearer  pole. 

When  alternating  currents  are  employed  on  the  line,  the 
lever  c  c'  must  be  adjusted  as  nearly  as  possible  in  the  middle 
of  the  space  between  n  and  n',  in  which  case  it  will  remain  on 
the  side  to  which  it  was  last  attracted,  until  a  current  in  the 
opposite  direction  moves  it  to  the  other  side. 


The  space  between  _ne  magnet  poles  n,  n',  and  the  contacts 
of  the  armature  lever  at  D  and  D',  are  shown  in  detail  in 
Fig.  334,  which  is  a  plan  of  the  preceding  figure.  The  bind- 
ing posts,  for  the  line  battery  are  shown  at  L  B,  and  those 
for  the  local  battery  at  O,  B.  The  dotted  lines  show  the  con- 
nections. 

Since  the  polarized  relay  dispenses  with  the  retractile 
spring,  it  is  far  more  sensitive  than  the  ordinary  instrument. 


524 


A  DICTIONARY  OP  ELECTRICAL 


Once  adjusted  no  further  regulation  is  required,  in  which  re- 
spect, it  differs  very  decidedly  from  non-polarized  relays. 

Reluctance,  Magnetic  —(See  Magnetic  Re- 
luctance.) 


Repeaters,    Telegraphic 


— Teregraphic    de- 


vices, whereby  the  relay,  sounder,  or  registering  apparatus 
is  caused  to  repeat  the  signals  received,  by  opening  and  clos- 
ing another  circuit  with  which  it  is  suitably  connected. 


Fig.  3S5. 

Repeaters  are  employed  to  establish  direct  communication 
between  very  distant  stations,  or  to  connect  branch  lines  to 
the  main  line. 

Fig.  335,  shows  Wood's  Button  Repeater.  This  repeater 
consists  simply  of  a  three-point-switch  L,  capable  of  being 


WORDS,  TERMS  AND  PHRASES. 


525 


placed  on  the  points  1,  2  and  3  ;  and  a  ground  switch  at  4. 
The  circuits  are  arranged  between  the  sounders  S,  S',  relays 
M,  M',  main  batteries 
B,  B',  and  the  two  main 
lines  E  and  W,  in  the 
manner  shown. 

If  the  lever  L,  is  in 
the  position  shown  in 
the  drawing,  the  lines 
E  and  W,  form  inde- 
pendent circuits. 

If  the  ground  switch 
4  is  closed,  and  the 
lever  L  is  placed  on  2, 
2,  the  eastern  line  re- 
peats into  the  western. 
If  the  lever  L  is  placed 
on  the  plates  3,  3,  the 
western  line  repeats 
into  the  eastern. 

This  repeater  is  non- 
automatic  and  can  be 
worked  in  but  one  di- 
rection ;  morever,  it  re- 
quires the  services  of  an 
attendant. 

The  automatic  repeat- 
er can  be  operated  in 
both  directions,  and  dis- 
penses with  the  con- 
stant services  of  an  at- 
tendant at  the  repeat- 
ing station. 

In  sending  a  dispatch 
through  a  repeater,  the  dots  and  dashes  are  prolonged  so  as  to 


526 


A  DICTIONAEY  OF   ELECTRICAL 


give  the  lever  of  the  repeating  instrument  time  in  which 
to  move  backwards  and  forwards. 

In  Hacks'  Automatic  Button  Repeater,  shown  in  Fig.  336, 
the  switch  or  circuit  changer  is  automatic  in  its  action. 

The  relay  magnets  are  shown  at  M,  M',  the  sounders  at  R, 
and  R' ;  /,  /',  are  platinum  contacts  operated  by  levers  I  and  I, 
and  L  and  L'  are  Extra  Local  Magnets,  that  act  on  armatures 
placed  directly  opposite  the  armatures  of  the  relay  magnets. 
The  extra  local  magnet  L  is  cut 
out  of  the  circuit  of  B',  the  Extra 
Local  Battery,  when  the  main  cir- 
cuit is  broken,  and  the  armature  is 
in  contact  with  c.  As  soon  as  this 
happens,  however,  the  spring  s, 
drawing  away  the  armature,  and 
thus  opening  the  short  circuit  of 
no  resistance  between  c  and  a, 
establishes  a  circuit  through  L. 
On  a  coming  in  contact  with  c, 
the  circuit  is  again  broken.  The 
tension  of  the  spring  s  is  so  regu- 
lated that  a  very  rapid  vibration 
of  a  is  so  constantly  maintained, 
that  it  is  impossible  to  close  the 
main  circuit  when  L  is  not  cut 
out.  The  armature  a  will  there- 
fore respond  to  very  weak  impulses 
of  the  relay  magnet. 

On  breaking  the  western  main 
circuit  N,  the  lever  a  vibrates 
very  rapidly.  The  lever  I,  of  the  sounder  R,  first  breaks 
the  circuit  of  L,  and  afterwards  that  of  the  eastern  main 
circuit  E,  which  passes  though  M.  Both  L'  and  M',  be- 
ing broken,  a  slight  tension  of  s',  will  hold  a,  in  place,  thus 
avoiding  the  breaking  of  the  western  main  circuit  through 


Fig.  337. 


WOIIDS,  TERMS  AND  PHRASES.  527 

the  closing  of  the  local  circuit  through  R.      On  the  closing  of 
the  western  circuit,  the  reverse  of  these  operations  occur. 

The  author  has  taken  the  above  explanation  mainly  from 
Pope's  work  on  "  Modern  Practice  of  the  Electric  Tele- 
graph." 

Replenisbcr,  Thomson'* A  static  influ- 
ence machine  devised  by  Sir  Wm.  Thomson  for  charging  the 
quadrants  of  his  quadrant  electrometer. 

Two  brass  carriers  C  and  D,  shown  in  Fig.  337,  are  ec- 
centrically fixed  to  the  end  of  the  vulcanite  rod  E,  which  is 
capable  of  rotation  by  the  thumb  screw  at  M,  in  the  direction 
shown  by  the  arrow.  Hollow  metal  half  cylinders,  A  and  B, 
act  as  inductors,  a  strip  of  brass  fixed  around  the  edges  of  a 
piece  of  vulcanite  P,  connecting  the  metallic  springs  S  and  S',  as 
shown.  The  action  of  the  replenisher  is  readily  understood 
from  the  following  considerations,  as  suggested  by  Ayrton  in 
his  "  Practical  Electricity"  : 

A  and  B,  Fig.  338,  are  two  insulated  hollow  metallic  vessels 
having  a  small  difference  of  potential  between  them,  A,  being 
the  higher.  C  and  D,  are  two  small  uncharged  conductors 
held  by  insulating  strings.  If  C  and  D  be  held  near  A  and 
B,  as  shown,  the  potential  of  C  will,  by  induction,  be  raised 
somewhat  above  that  of  D,  so  that  when  connected  by  a  con- 
ductor, such  as  the  metallic  wire  W,  a  small  quantity  of 
positive  electricity  will  flow  from  C  to  D,  thus  leaving  D 
positively,  and  C  negatively  charged. 

If,  now,  C  and  D,  are  removed  from  W  and  placed  in  the 
bottom  of  B  and  A,  as  shown  in  Fig.  339,  the  difference  of 
potential  between  A  and  B,  will  be  thereby  increased,  and  if 
they  are  then  withdrawn,  and  totally  discharged,  and  again 
placed  in  the  first  position  shown,  an  additional  charge 
can  be  given  to  A  and  B,  and  this  can  be  repeated  as  often  as 
desired. 

In  the  replenisher,  A  and  B  correspond  to  the  vessels  A 
and  B ;  the  brass  carriers  C  and  D,  to  the  balls  C  and  D, 


528 


A  DICTIONARY  OF  ELECTRICAL 


and  the  spring  S  S,  and  M,  to  the  wire  W.  No  initial  charge 
-need  be  given  to  A  and  B,  since  they  are  invariably  found 
to  be  at  a  sufficient  difference  of  potential  to  build  up  the 
charge. 

Residual  Atmosphere. — (See  Atmosphere,  Residual.) 
Residual  Charge.— (See  Charge,  Residual.) 
Residual   Magnetism. — The  magnetism  remaining  in 
the  core  of  an  electro-magnet  on  the  opening  of  the  magnetiz- 
ing circuit. 

Resin. — A  general  term  applied  to  a  variety  of  dried 
juices  of  vegetable  origin. 

Resins  are,  in  general,  transparent,  inflammable  solids, 
soluble  in  alcohol,  and  are  non-conductors  of  electricity.  Rosin 
is  one  of  the  varieties  of  resin. 


Fig.  358. 


Fig.  339. 


Resinous  Electricity.— A  term  formerly  employed  in 
place  of  negative  electricity. 

It  was  at  one  time  believed  that  all  resinous  substances  are 
negatively  electrified  by  friction.  This  we  now  know  to  be 
untrue,  the  nature  of  electrification  depending  as  much  on 
the  character  of  the  rubber,  as  on  the  character  of  the  thing 


WORDS,  TERMS  AND  PHRASES. 


529 


rubbed.  Thus  resins  rubbed  with  cotton,  flannel  or  silk,  be- 
come negatively  excited,  but  rubbed  with  sulphur  or  gun- 
cotton,  positively  excited.  The  terms  positive  and  negative 
are  now  exclusively  employed. 

Resistance  Box. — A  box  containing  a  number  of  coils  of 
known  resistances  employed  for  determining  the  value  of  an 
unknown  resistance.  (See  Box,  Resistance.  Balance,  Electric, 
Box  Form  of.) 

Resistance  Coil.— A  coil  of  insulated  wire  of  known 
resistance  doubled  on  itself  before  winding,  so  as  to  neutralize 
the  external  effects  of  its  own  magnetic  field.  (See  Coils,  Re- 
sistance.) 


Resistance     Coil,     Standard 


—A     coil 


the  resistance  of  which  is  that  of  the  standard  ohm. 

The  standard  ohm,  as  issued 
by  the  Electric  Standards  Com- 
mittee of  England,  has  the 
form  shown  in  Fig.  340.  The 
coil  of  wire  is  formed  of  an 
alloy  of  platinum  and  silver, 
insulated  by  silk  covering  and 
melted  paraffine.  Its  ends  are 
soldered  to  thick  copper  rods 
r,  r',  for  ready  connection  with 
mercury  cups.  The  coil  is  at 
B.  The  space  above  it  at  A  is 
filled  with  paraffin,  except  at 
the  opening  t,  which  is  provided  for  the  insertion  of  a  ther- 
mometer 

Resistance,  Effect  of  Heat  on  Electric  — 
Nearly  all  metallic  conductors  have  their  electric  resistance 
increased  by  an  increase  of  temperature. 

The  carbon  conductor  of  an  electric  incandescent  lamp  on  the 
contrary,  has  its  resistance  derroasfv I  \\ -lion  raised  to  electric 


Fig.  3!tO. 


530 


A  DICTIONARY  OF  ELECTRICA^ 


incandescence.     The  decrease  amounts  to  about  three-eighths 
of  its  resistance  when  cold. 

The  effects  of  heat  on  electric  resistance  may  be  sum- 
marized as  follows : 

(1)  The  electric  resistance  of  metallic  conductors  increases 
as  the  temperature  rises.     (Carbon  is  an  exception). 

(2)  The  electric  resistance  of  electrolytes  decreases  as  the 
temperature  rises. 

(3)  The  electric  resistance  of  dielectrics  and  non-conductors 
decreases  as  the  temperature  rises. 

Resistance  and  Conductivity  of  Pure  Copper   at  Different 
Temperatures. 


Centigrade 
Tempera- 
ture. 

Resistance. 

Conductivity, 

Centigrade 
Tempera- 
ture. 

Resistance. 

Conductivity. 

0° 

1.00000 

1.00000 

16° 

1.06168 

.94190 

1 

1.00381 

.99624 

17 

1.06563 

.93841 

2 

1.00756 

.99250 

18 

1.06959 

.93494 

3 

1.01135 

.98878 

19 

1.07356 

.93148 

4 

1.01515 

.98508 

20 

1.07742 

.92814 

5 

1.01896 

.98139 

21 

1.08164 

.62452 

6 

1.02280 

.97771 

22 

1.08553 

.92121 

7 

1.02663 

.97406 

23 

1.08954 

.91782 

8 

1.03048 

.97042 

24 

1.09365 

.91445 

9 

1.03435 

.96679 

25 

1.09763 

.91110 

10 

1.03822 

.96319 

26 

1.10161 

.90776 

11 

1.04199 

.95970 

27 

1.10567 

.90443 

12 

1.04599 

.95603 

28 

1.11972 

.90113 

13 

1.04990 

.95247 

29 

1.11382 

.89784 

14 

1.05406 

.94893 

30 

1.11782 

.89457 

15 

1.05774 

.94541 

(Latimer  Clark.) 

The  following  table  from  Matthiessen's  measurements  giv 
the  relative  resistances  of  eqvial  lengths  and  cross  soclioi: 


WORDS,  TERMS  AND  PHRASES. 


531 


of  different  substances  as  compared  with  silver.     The  sub- 
stances are  chemically  pure. 

Legal  Microhms. 


NAMES  OP  METAL. 

Resistance  in  Microhms  atO°  C. 

Relative 

Resistance. 

Cubic 
Centimetre. 

Cubic  inch. 

Silver,  annealed  
Copper,  annealed  
Silver,  hard  drawn  
Copper,  hard  drawn.  .  . 
Gold,  annealed 

1.504 
1.598 
1.634 
1.634 
2.058 
2.094 
2.912 
5.626 
9.057 
9.716 
12.47 
13.21 
19.63 
20.93 
35.50 
94.32 
131.2 

0.5921 
0.6292 
0.6433 
0.6433 
0.8102 
0.8247 
1.1470 
2.215 
3.565 
3.825 
4.907 
5.202 
7.728 
8.240 
13.98 
37.15 
51.65 

1. 
1.063 
1.086 

1.086 
1.36'J 
1.393 
1.935 
3.741 
6.022 
6.460 
8.285 
8.784 
13.05 
13.92 
23.60 
62.73 
87.23 

Gold,  hard  drawn  
Aluminium,  annealed  . 
Zinc,  pressed  
Platinum,  annealed... 
Iron,  annealed  . 

Nickel,  annealed 

Tin,  pressed 

Lead,  pressed 

German  Silver 

Antimony,  pressed  
Mercury 

Bismuth,  pressed  

(Ayrton.) 

The  above  resistances  are  for  chemically  pure  substances 
only.  Slight  impurities  produce  very  considerable  changes 
in  the  resistance. 


Resistance,  Electric The  ratio  between 

the  electro-motive  force  of  a  circuit  and  the  current  that 
passes  therein. 

Ordinarily  the  resistance  of  a  circuit  may  be  conveniently 
regarded  as  that  which  opposes  or  resists  the  passage  of  the 


532  A  DICTIONARY  OF  ELECTRICAL, 

current.  Strictly  speaking,  however,  this  is  not  true,  since 
from  Ohm's  law  (See  Ohm's  Law), 

E 

C  =  — ,  from  which  we  obtain 
R 
E 
R  =  — ,  which  shows  that  resistance  is  a  ratio  between 

C 

the  electro-motive  force  that  causes  the  current  and  the 
current  so  produced. 

Resistance  may  be  expressed  as  a  velocity.    The  dimensions 
of  resistance  in  terms  of  the  electro-magnetic  units  are 
L 

T 

(See  Units,  Electro-Magnetic.)  But  these  are  the  dimensions  of 
a  velocity  which  is  the  ratio  of  the  distance  passed  over  in  unit 
time.  Resistance  may  therefore  be  expressed  as  a  velocity. 

"  The  resistance  known  as  '  one  ohm'  is  intended  to  be  109 
absolute  electro-magnetic  units,  and  therefore  is  represented 
by  a  velocity  of  109  centimetres  or  ten  million  metres  (one 
earth-quadrant)  per  second  " — Sylvanus  Thompson. 

Resistance  may  be  represented  by  a  velocity,  one  ohm  being 
the  resistance  of  a  wire,  which,  if  moved  through  a  unit  field 
of  force  at  the  rate  of  ten  million  (109)  centimetres  per  second 
will  have  a  current  of  one  ampere  generated  in  it.  (See  Ohmic 
Resistance.  Spurious  Resistance. 

The  unit  of  resistance  is  the  ohm.  Its  true  value,  as  has 
been  shown  by  careful  measurements,  is  not  exactly  equal  to 
109  centimetres  per  second. 

Resistance,  Electrie of  Liquids  .—The  resist- 
ance offered  by  a  liquid  mass  to  the  passage  of  an  electric 
current. 

As  a  rule  the  electric  resistance  of  a  liquid  is  enormously 
higher  than  that  of  metallic  bodies,  with  the  single  exception 
of  mercury. 

To  determine  the  resistance  ®f  a  liquid,  a  section  is  taken 


WORDS,  TERMS  AND  PHRASES. 


between  two  parallel  metallic  plates  A  and  B,  Fig.  341, 
placed  as  shown  in  the  figure,  and  an  electric  current  is 
passed  between  them.  In  order  to  avoid  the  effect  of  a  spur- 
ious resistance,  due  to  a  counter  electro-motive  force,  it  is 
necessary  to  use  plates  at  A  and  B,  of  metals  that  are  not 
acted  on  chemically  by  the  liquid  on  the  passage  of  the  current. 
(See  Counter  Electro-Motive  Force.  Spurious  Resistance.) 
In  order  to  more  accurately  vary  the  size  of  the  plates 
immersed  in  the  liquid,  and  hence  the  area  of  cross  section  of 
the  liquid  conductor,  as  well  as  the  distance  between  the 
plates,  the  apparatus  shown  in  Fig.  342  may  be  used,  in  which 
these  distances  are  readily  adjustable,  as  shown. 

Resistance,  Magnetic (See  Magnetic  Resistance.) 

Resistance,  Measurement  of Methods  em- 
ployed for  determining  the  resistance  of 
any  circuit  or  part  of  a  circuit. 

Numerous  methods  are  employed   for 
this  purpose.     Among  these  are  : 

(1)  The  use  of  a  Resistance  Box  with  a 
Wheatstone's  Bridge,  by  opposing  or  bal- 
ancing the  unknown  resistance  against  a 
known  resistance.     (See  Balance,  Wheat- 
stone's.) 

(2)  With  the  Differential  Galvanometer. 
(See   Galvanometer,  Differential.) 

(3)  By  the  Method  of  Substitution. 

(4)  By  a  Comparison  of  the  Deflections 
of  a  Galvanometer. 

Method  of  Substitution— A  resistance 
box  R,  Fig.  343,  galvanometer  G,  and  the 
resistance  x,  that  is  to  be  measured, 
are  placed  in  the  direct  circuit  of  the 
battery  B  by  means  of  conductors  of  such  thick  wire  that 
their  resistance  can  be  neglected.  The  deflection  of  the  gal- 
vanometer is  first  measured  with  x  in  circuit,  and  no  resist- 


Fig.  Ski. 


534 


A  DICTIONARY  OF   ELECTRICAL 


ance  in  the  box  R.  The  resistance  x  is  then  cut  out  of  the 
circuit  by  placing  a  thick  copper  wire  across  the  terminals  of 
the  mercury  cups  at  in,  m',  and  resistances  unplugged  in  R, 
until  the  same  deflection  is  obtained.  Then,  if  the  electro- 


Fig.  si,s. 

motive  force  of  the  battery  has  remained  constant,  the  resist- 
ances unplugged  equal  the  unknown  resistance. 

For  full  description  of  the  various  methods  of  determining 
resistance  the  reader  is  referred  to  "  Ayrton's  Practical  Elec- 
tricity,1' "Kempe's  Handbook  of  Testing,"  or  other  standard 
electrical  books. 

Resistance,  Olmi- 

Ic (See 

Ohmic  Resistance.} 
G      Resistance,  Spur- 
ious  (See 

Spurious  Resistance.) 
Resistance,  Tab- 
les of Tables  in 

Fig.  31,3.  which  the  resistance  of 

equal  lengths  and  cross  sections  of  different  substances  is 
given  in  ohms,  or  other  units  of  resistance  : 


WORDS,  TKKMS   AND   PHRASES. 


535 


RESISTANCE. 

Resistance  of  Wires  of  Pure  Annealed   Copper  at  0"   C. 
(Density  =  8.9.) 


fi    isi 

ii  m 

53  ,    £  ° 

Length  in 
Metres  per 
Kilogramme. 
(Bare  Wire). 

Resistance  of  Wire  of  Pure  Annealed 
Copper  at  0°  C. 

Ohms 
per 
Kilometre. 

Metres 
per 
Ohm. 

Ohms 
per 
Kilogramme. 

5         175 

5.7 

.8 

1230.5 

.00456 

4.4     135.28 

7.4 

1.06 

944.38 

.00784 

3.9     106.35 

9.5 

1.35 

722 

.0128 

3.4       80.8 

12.5 

1.80 

563.92 

.0222 

3       j   62.93 

16 

2.3 

439.07 

.0365 

2.7       51 

19.8 

2.8 

355.65 

.0557 

2.4       40.23 

25 

3.6 

281 

.088 

2.2    i    33.82 

29 

4.2 

236.08 

.123 

2           27.95 

36 

5.1 

195.15 

.185 

1.8       22.7 

44 

6.3 

158.08 

.278 

1.6       17.89 

56 

8 

124.9 

.448 

1.5       15.75 

63 

9.1 

109.75 

.574 

1.4 

13.7 

73 

10.5 

95.651 

.763 

1.3 

11.84 

85 

12 

82.42 

1.03 

1.2 

10.06 

100 

14 

70.247 

1.42 

1.1 

8.47 

119 

17 

59.024 

2.02 

1 

6.99 

144 

20 

48  782 

2.95 

.9 

5.66 

178 

25 

39.515 

4.19 

.8 

4.47 

225 

32 

31.225 

7.21 

.7 

2.83 

294 

42 

23.9 

12.3 

.6 

2.52 

400 

57 

17.56 

22.78 

.5 

1.74 

576 

81 

12.305 

46.81 

.4 

1.175 

902 

122.4 

8.173 

110.41 

.34 

.808 

1251 

177.9 

5.622 

222.55 

.3 

.7181 

1607 

228.5 

4.377 

367.2 

.24 

.4026 

2508 

357 

2.801 

895.36 

.2 

.2797 

3614 

514 

1.945 

1,857.6 

.16 

.179 

5590 

803.1 

1.245 

4,489 

.12 

.1007 

9929 

1428 

.7 

14,179 

.1 

.0699 

14369 

2056 

.486 

29,549 

.08 

.0447 

24570 

3213 

.311 

78,943 

.06 

.0252 

39824 

5713 

.173 

227,515 

.04 

.0112 

88878 

12848 

.078 

1,142,405 

(Hospitalier. ,) 


536 


A  DICTIONARY  OP  ELECTRICAL 


Table  of  Conducting  Powers  and  Resistances  in  Ohms. 


NAMES  op  METALS. 


Silver,  annealed 

Silver,  hard  drawn... 

Copper,  annealed 

Copper,  hard  drawn. . 

Gold,  annealed 

Gold,  hard  drawn .... 

Aluminium,  annealed 

Zinc,  pressed 

Platinum,  annealed. . 

Iron,  annealed 

Nickel,  annealed.  .. 

Tin,  pressed 

Lead,  pressed 

Antimony,  pressed. . . 

Bismuth,  pressed..  . 

Mercury,  liquid 

Platinum-silver,  al- 
loy, hard  or  annealed 

German  silver,  hard 
or  annealed 

Gold,  silver,  alloy, 
V>ard  or  annealed. . . . 


16.81 
13.11 
12.36 
8.32 
4.62 
1.24 


ES? 


III 


0.2214 


0.2064 
0.2106 
0.5849 
0.5950 


0.5710 
3.536 
1.2425 
1.0785 
1.317 


5.054 
18.740 


2.391 


0.1544 
0.1689 
0.1440 


0.4150 
0.05759 


2.464 
0.7522 


0.9184 
2.257 


13.071 
2.959 
1.850 
1.668 


g.9 


III 


9.151 
9.718 
9.940 
12.52 
12.74 
17.72 
32.22 
55.09 
59.40 
75.78 


216.0 
798.0 
600.0 

143.35 
127.32 
66.10 


0.01937 
0.02103 


. 
0.02650 


0.03751 
0.07244 
0.1166 


0.1604 
0.1701 
0.2527 
0.4571 
1.689 
1.270 

0.3140 


0.365 
0.387 
0.389 
0.354 
0.072 

0.031 
0.044 
0.065 


(Jenkin.) 

When  several  resistances  are  placed  in  series  in  any  circuit, 
by  measuring  the  difference  of  potential  at  their  terminals, 
their  values  can  be  determined  by  simple  calculation,  being 
directly  proportional  to  these  differences  of  potential.  This 
method  in  especially  applicable  to  the  measurement  of  such 
low  resistances  as  the  armatures  of  dynamo  electric  machines. 

Re§ultant. — In  mechanics,  a  single  force  that  represents 


WORDS,  TERMS  AND  PHRA.SES.  537 

in  direction  and  intensity  the  effects  of  two  or  more  forces 
acting  in  different  directions. 

Retardation.— A  decrease  in  the  speed  of  telegraphic 
signaling  caused  by  the  induction  of  the  line  conductor  on 
itself,  and  the  induction  between  it  and  neighboring  con- 
ductors. 

Retardation  in  signaling  is  produced  by  the  following 
causes : 

(1)  Self-induction  which  produces   extra  currents.      (See 
Self-induction.     Currents,  Extra.} 

The  extra  current  on  making,  retards  the  beginning  of  the 
signal,  and  the  extra  current  on  breaking,  retards  its  stopping. 

(2)  Mutual  Induction  between  the  line  conductor  and  neigh- 
boring conductors.     The  line  must  receive  a  certain  charge 
before  a  current  sent  into  it  at  one  end  can  produce  a  signal  at 
the  other  end.     This  charge  will  depend  on  the  length  and 
surface  of  the  wire,  on  its  neighborhood  to  the  earth  or  other 
wires,  and  on  the  nature  of  the  insulating  material  between  it 
and  the  neighboring  conductor.    This  results  in  a  charge  given 
to  the  wire  which  is  lost  as  a  current  for  signaling.     The 
greater  the  electrostatic  capacity  of  the  line  wire,  the  greater 
will  be  the  retardation  in  signaling.     (See  Capacity,  Specific 
Inductive.    Dielectric.     Electrostatic  Capacity.) 

(3)  The  Magnetic  Inertia  or  Lag,  or  the  time  required  to 
magnetize  or  demag-netize  the  core  of  the  electro-magnetic 
receptive  devices  used  on  the  line. 

Rctentivity,  Magnetic  — A  term  proposed  by 

Lament  in  place  of  coercive  force,  or  the  power  possessed  by 
a  magnetizable  substance  of  resisting  magnetization  or 
demagnetization.  (See  Coercive  Force.) 

Return  Shock  or  Stroke.    (See  Back  Stroke.) 

Reverse  Induced  Current.— The  current  produced  by 
self-induction  in  a  circuit  at  the  moment  of  completing  the 
circuit.  (See  Extra  Current.) 


538  A  DICTIONARY  OF  ELECTKICAL 

Reversing  Gear  of  Electric  Motor. — Apparatus  for 
reversing  the  direction  of  the  current  through  an  electric 
motor,  and,  consequently,  the  direction  of  its  rotation.  (See 
Railroad  or  Railway,  Electric.) 

Reversing  Key.— (See  Key,  Reversing.) 

Rheochord. — (See  Rheostat.) 

Rlieometer. — A  term  formerly  employed  for  any  device 
for  measuring  the  strength  of  a  current.  (Now  obsolete  and 
replaced  by  the  word  Galvanometer.) 

Rheomotor. — A  term  formerly  employed  to  designate 
any  electric  source.  (Now  obsolete  and  replaced  by  the  various 
names  of  the  different  electric  sources.  (See  Source,  Electric.) 

Rheophore. — A  term  formerly  employed  to  indicate  a 
portion  of  a  circuit  conveying  a  current  and  capable  of  deflect- 
ing a  magnetic  needle  placed  near  it.  (Now  obsolete.) 

Rheoscope. — A  term  formerly  employed  in  place  of  the 
present  word  Galvanoscope,  for  an  instrument  intended  to 
show  the  presence  of  a  current,  or  its  direction,  but  not  to 
measure  its  strength.  (Now  obsolete.) 

Rheo§tat. — A  term  signifying  any  adjustable  resistance. 

A  rheostat  enables  the  resistance  to  be  brought  to  a  stand, 
i.  e.,  to  a  fixed  value  ;  hence  the  name. 

The  term  rheostat  is  applied  generally  to  a  readily  variable 
resistance,  the  varying  values  of  which  are  known. 

Rheostat,  Wheatstone's A  form  of  appa- 
ratus sometimes  employed  for  an  adjustable  resistance. 

This  apparatus  is  very  seldom  employed  in  accurate  work. 

The  parallel  cylinders  A  and  B,  Fig.  344,  are  respectively  of 
conducting  and  non-conducting  materials,  the  bare  wire  on 
which  can  be  wound  from  either  cylinder  to  the  other.  When 
introduced  into  a  circuit,  only  the  resistance  of  the  portions 
of  the  wire  on  B  is  introduced  into  the  circuit,  since  the  bare 
wire  on  A  is  short  circuited  by  the  metallic  cylinder.  This 


WORDS,  TERMS  AND   PHRASES. 


538 


rheostat  is  seldom  employed  in  accurate   measurements  ow- 
ing to  the  difficulty  of  invariably  obtaining  reliable  contacts. 

RhcoKtatic  Machine. — A  machine  devised  by  Plant6  in 
which  continuous  static  effects  of  considerable  intensity  are 
obtained  by  charging  a  number  of  condensers  in  multiple  arc 
and  discharging  them  in  series. 

The  condensers  are  charged  by  connecting  them  with  a 
number  of  secondary 
or  storage  batteries- 

Rheo  tome  .—A 
term  formerly  em- 
ployed for  any  device 
by  means  of  which  a 
circuit  could  be  peri- 
odically interrupted. 
(Now  obsolete  and  re- 
placed by  Interrupt- 
er.) 

Rheotrope.  —  A 
term  formerly  em- 
ployed for  any  device 
by  which  the  current 
could  be  reversed.  (Now  obsolete  and  replaced  by  Commuta- 
tor or  Current  Reverser.) 

Rhigolene.— A  volatile  hydro-carbon  obtained  during  the 
distillation  of  coal  oil,  and  employed  in  the  flashing,  or  treat- 
ment of  carbons.  (See  Flashing  of  Carbons.) 

Rhumbs  of  Compass.— The  thirty-two  points  of  the 
mariners'  compass.  (See  Points  of  Compass.) 

Rigidity,  Molecular Resistance  offered  by 

the  molecules  of  a  substance  to  rotation,  or  displacement. 

The  molecular  rigidity  of  a  magnetizable  substance  is  now 
generally  considered  to  be  the  cause  of  differences  of  coercive 


540  A  DICTIONARY  OP  ELECTRICAL 

force  or  magnetic  retentivity.  (See  Coercive  Force.  Reten- 
tivity,  Magnetic.) 

Rings,  \ohiliS (See  Metallochromes.) 

Rods,  Lightning (See  Lightning  Rods.) 

Rotation,  Electro  Magnetic (See  Accumu- 
lator. Disc,  Arago's.  Disc,  Faraday's.  Motors,  Electric.) 

Rotation,  magneto-Optic (See  Magneto- Optic 

Rotation. 

Rubber  of  Electrical  Machine.— A  cushion  of 
leather,  covered  with  an  electric  amalgam,  and  employed 
to  produce  electricity  by  its  friction  against  the  plate  or  cylin- 
der of  nfrictional  electric  machine.  (See  Machine,  Frictional. ) 

Ruhmkorff  Coils.— (See  Induction  Coils.) 

Saddles,  Telegraphic Brackets  placed  on  the 

top  of  telegraph  poles,  for  the  support  of  the  insulators. 

Saddle  brackets  are  usually  employed  for  the  wire  attached 
to  the  top  of  a  telegraph  pole.  (See  Poles,  Telegraphic.) 

Safety  Catch,  Safety  Device,  Safety  Fuse,  Safety 
Plug  or  Safety  Strip  for  Multiple  Circuits.— A  wire, 
bar,  plate,  or  strip  of  readily  fusible  metal,  capable  of  conduct- 
ing, without  fusing,  the  current  ordinarily  employed  on  the 
circuit,  but  which  fuses,  and  thus  breaks  the  circuit,  on  the 
passage  of  an  abnormal  current.  (See  Lamp,  Incandescent.) 

Safety  Device  for  Arc  Lamp,  or  Series  Circuits.— 

Mechanism  which  automatically  provides  a  path  for  the 
current  around  a  lamp,  or  other  faulty  electro-receptive  de- 
vice in  a  series  circuit,  and  thus  prevents  the  opening  of  the 
entire  circuit  on  the  failure  of  such  device  to  operate.  (See 
Lamp  Arc,  Electric.) 

Safety  Lamp,  Electric An  incandescent 

electric  tamp,  with  thoroughly  insulated  leads,  employed  m 


WORKS,  TERMS  AND  PHRASES.  541 

mines,  or  other  similar  places,  where  the  explosive  effects  of 
readily  ignitable  substances  are  to  be  feared.  Such  lamps  are 
often  directly  attached  to  a  portable  battery. 

Salts,  Electrolysis  of The  decomposition  of  a 

salt  into  its  electro  positive  and  negative  radicals  or  ions. 
(See  Electrolysis.) 

Saturation,  Magnetic The  maximum  mag- 
netization which  can  be  imparted  to  a  magnetic  substance. 

In  an  electro-magnet,  such  a  degree  of  magnetization,  that 
any  further  increase  of  the  magnetizing  current,  increases  the 
magnetic  intensity  only  to  the  comparatively  small  extent  of 
the  increase  of  the  magnetic  field  due  to  the  current  itself. 
(See  Magnetic  Saturation.) 

Scratch  Brush.— A  brush  furnished  with  metallic 
bristles,  and  employed  for  cleansing  the  surfaces  of  metallic 
objects  prior  to  their  being  electro-plated. 

Screen,  Methven's  Standard (See  Methven's 

Standard  Screen.) 

Screen  or  Shield,  Electric A  closed  con- 
ductor, placed  over  a  charged  body  to  screen  or  protect  it  from 
the  effects  of  external  electrostatic  fields. 

The  ability  of  a  closed,  hollow  conductor  to  act  as  a  screen, 
arises  from  the  fact  that  all  points  on  Its  inner  surface  are  at 
the  same  potential,  and  therefore  are  not  affected  by  an  in 
crease  or  decrease  in  the  potential  of  the  outside  of  the  con- 
ductor as  compared  with  that  of  the  earth.  (See  Net,  Fara- 
day's.) 

No  considerable  thickness  is  required  for  the  efficient  opera- 
tion of  an  electric  screen. 

Screen  or  Shield,  Magnetic  — (See  Magnetic 

Screen  or  Shield.) 

Screws,  Binding or  Binding  Posts  —  (See 

Binding  Posts.) 


543  A  DICTIONARY   OF   ELECTRICAL 

Seal,  Hermetical (See  Hermetical  Seal.) 

Search-Lights,    Electric (See   Lighthouse 

Illumination.) 

Secondary  Batteries.— Arrangements  of  voltaic  cells 
that  derive  their  differences  of  electric  potential  from  the 
action  of  an  electric  current  sent  through  them  from  a  sep- 
arate source.  (See  Storage  of  Electricity.) 

Secondary  Clocks.— (See  Clocks,  Secondary.) 

Secondary  Currents.— The  currents  induced  in  the 
secondary  coil  of  an  induction  apparatus.  (See  Induction 
Coils.) 

In  the  United  States  this  term  is  also  applied  to  the  cur- 
rents derived  from  secondary  batteries.  The  word  is  generally 
employed  m  the  former  sense. 

Secondary  Generators.— A  term  sometimes  employed 
for  transformers  or  converters.  (See  Transformers  or  Con- 
verters.) 

Seismograph,  Electric An  apparatus  for 

electrically  recording  the   direction  and  intensity  of  earth- 
quake shocks 

Selenium.— A  comparatively  rare  element  generally 
found  associated  with  sulphur. 

Selenium  Cell. — A  photo-electric  couple  consisting  of 
selenium  in  combination  with  another  metal  usuahy  copper, 
and  capable  of  producing  a  current  by  the  direct  action  of 
light. 

Selenium  Cell,  or  Resistance.— A  mass  o'  crystalline 
selenium,  the  resistance  of  which  is  reduced  by  placing  it  in 

leform  of  narrow  strips  between  the  edges  of  broad  conduct- 
ing plates  of  brass. 

The  selenium  employed  for  this  purpose  is  the  vitreous 
variety,  which  has  been  fused  and  maintained  for  several 


WORDS,  TERMS  AND  PHRASES.  543 

hours  at  about  220°  C.  by  means  of  which  its  resistance  is 
reduced. 

By  exposure  to  sun-light,  the  resistance  of  a  selenium  cell 
is  decreased  fully  one-naif  its  resistance  in  the  dark.  The 
selenium  cell  is  used  in  the  Photophone  (See  Photophone.) 

Selenium  Eye.— An  artificial  eye  in  which  a  selenium 
resistance  takes  the  place  of  the  retina  and  two  slides  the 
place  of  the  eyelids. 

The  selenium  resistance  is  placed  in  the  circuit  of  a  battery 
and  a  galvanometer.  When  the  slides  L,L,  Fig.  345,  are  shut, 
the  galvanometer  deflection  is  less  than  when  they  are  open. 

The  opening  of 
the  aperture  be- 
tween the  slides 
L,  L,  may  be 

automatically  (\Q)  "">^  sj 

accomplished  by 
the  action  of  the 
light  itself,  by 
moving  them  by 
an  electro  -  mag-  Fig.  31,5. 

net  placed  in  the  circuit  of  a  local  battery,  and  a  selenium 
resistance  so  arranged  that  when  light  falls  on  the  selenium 
resistance,  the  slides  L,  L,  are  moved  together,  and  when  the 
amount  of  such  light  is  small,  they  are  moved  apart.  In  this 
way,  there  is  obtained  a  device  roughly  resembling  the  dilata- 
tion or  contraction  of  the  pupil  of  the  eye,  from  the  action  of 
light  on  the  iris. — (See  Photometer,  Selenium.) 

Self-induction.— The  induction  of  a  current  on  itself,  as 
distinguished  from  the  induction  it  produces  in  neighboring 
conductors.  (See  Currents,  Extra.) 

Self-induction,  Coefficient   of  —  —A  number 

representing  the  value  of  the  induction  produced  by  a  circuit 
on  itself, 


544  A  DICTIONARY  OF  ELECTRICAL 

The  coefficient  of  self-induction  varies  with  the  shape  of  the 
circuit,  and  increases  with  the  number  of  coils  or  turns  in  the 
circuit.  The  retardation  in  long  telegraph  lines,  where  num- 
erous coils  of  wire  are  used,  or  where  there  are  long  cables,  is 
due  to  self-induction  as  well  as  to  induction  in  neighboring 
conductors. 

According  to  Helmholtz,  as  phrased  by  Sylvanus  Thomp- 
son, "  The  self  induction  in  a  circuit  on  making  contact  has 
the  effect  of  diminishing  the  strength  of  the  current  by  a 
quantity,  the  logarithm  of  whose  reciprocal  is  inversely  pro- 
portional to 'the  coefficient  of  self-induction,  and  directly 
proportional  to  the  resistance  of  the  circuit,  and  to  the  time 
that  has  elapsed  since  making  the  circuit." 

Self-Recording  Magnetometer.  —  (See  Magneto- 
graph.) 

Self-Winding  Clocks.— (See  Clocks,  Self -Winding.} 

Semaphore. — A  vai'iety  of  signal  apparatus  employed  in 
railroad  block  systems. 

The  semaphore  used  on  the  Pennsylvania  Railroad  consists 
of  a  wooden  post,  in  the  neighborhood  of  twenty  feet  in  height, 
on  which  a  wooden  arm  or  blade,  six  feet  in  length  and  a  foot 
in  width  is  displayed.  When  the  block  is  cleari  the  arm  is 
placed  pointing  downwards  at  an  angle  of  75 "  with  the  horizon- 
tal by  day,  or  the  semaphore  displays  a  white  light  at  night. 
"When  the  block  is  not  clear,  the  arm  or  blade  i?  placed  in  a 
horizontal  position  by  day,  or  displays  a  red  light  at  night. 
(See  Block  Signals.) 

Sender,  Zinc (See  Zinc  Sender.) 

Sensibility  of  Galvanometer.— The  readiness  and  ex- 
tent to  which  the  needle  of  a  galvanometer  responds  to  the 
passage  of  an  electric  current  through  its  coils.  (See  Galvan- 
ometers.) 

Separate  Touch,  Magnetization  by (See 

Methods  of  Magnetization  by  Touch.  Separate. } 


WORDS,  TERMS  AND  PHRASES. 


545 


Separately  Excited  Dynamo  Electric  Machine.— 

A  dynamo  electric  machine,  whose  field  coils  are  excited  by 
means  of  a  source  external  to  the  machine.  (See  Dynamo 
Electric  Machine,  Separately  Excited.) 

Series  Circuit§. — (See  Circuits,  Varieties  of.) 

Series  Connections.— The  connection  of  a  number  of 
separate  electric  sources,  or  electro-receptive  devices,  or  cir- 
cuits so  that  the  current  passes  successively  from  the  first  to 
the  last  in  the  circuit,  (See  Circuits,  Varieties  of.) 

Series-Multiple  Circuit.— (See   Circuits,  Varieties  of.) 

Series,  Tliermo-Electric (See  Thermo-Electric 

Series.) 


Shackle,  Telegraphic 

lation  employed  on 
a  telegraph  pole  in 
order  to  confine  to 
one  point  the  strain 
caused  by  a  wire 
leaving  the  insula- 
tor at  a  sharp  angle. 
(See  Poles,  Tele- 
graphic.) 

Shadow,  Elec- 
tric,   or    Molec- 


—  A  special  form  of  insu- 


Fiff.  3!>6. 


ular The  comparatively  dark  space  on  those  parts 

of  the  walls  of  Crookes'  tubes,  which  have  been  protected 
from  molecular  bombardment  by  suitably  placed  screens. 

If  a,  in  the  Crookes'  tube 'shown  in  Fig.  346,  be  connected 
with  the  negative  pole  of  any  electric  source,  and  the  cross 
shaped  mass  of  aluminium  at  b,  be  connected  with  the  posi- 
tive electrode,  on  the  passage  of  a  series  of  discharges,  phos- 
phorescence is  produced  by  the  molecular  bombardment  from 
a,  in  all  parts  of  the  vessel  opposite  a,  except  those  lying  in 


546  A  DICTIONARY  OF  ELECTRICAL 

the  projection  of  its  geometrical  shadow.  (See  Phosphores- 
cence, Electric.) 

Shadow  Photometer.— (See  Photometer,  Shadow.) 

Sheet,  Current The  sheet  into  which  a  current 

spreads  when  the  wires  of  any  source  are  connected  at  any 
two  points  near  the  middle  of  a  very  large  and  thin  conductor. 

A  continuous  electric  current  flows  through  the  entire  mass 
of  a  conductor,  not  in  any  single  line  of  direction,  but,  if  the 
terminals  of  any  source  are  connected  to  neighboring  parts  of 
a  greatly  extended  thin  conductor,  the  current  spreads  out  in  a 
thin  sheet  known  as  a  current  sheet,  and  instead  of  flowing  in  a 
straight  line  between  the  points,  spreads  over  the  plate  in 
curved  lines  of  flow,  which,  so  far  as  shape  is  concerned,  are 
not  unlike  the  lines  of  magnetic  force. 

Shells,  Magnetic  —       •  —(See  Magnetic  Shells.) 

Shellae. — A  resinous  substance  possessing  valuable  insul- 
ating properties,  which  is  exuded  from  the  roots  and  branches 
of  certain  tropical  plants. 

The  specific  inductive  capacity  of  shellac  as  compared  with 
air  is  2.74. 

Shield,  magnetic for  Watches.— A  hollow  case 

of  iron,  in  which  a  watch  is  permanently  kept,  in  order  to 
seield  it  from  the  influence  of  external  magnetic  fields.  (See 
Magnetic  Screens  or  Shields.) 

Ships,  Protection  of from  Lightning  Strokes. 

—(See  Lightning  Rods  for  Ships.) 

Ship's  Sheathing,  Electric  Protection  of 

—(See  Metals,  Electric  Protection  of.) 

Shock,  Electric  —  —A  physiological  effect  produced 
on  animals  by  the  passage  through  them  of  an  electric  cur- 
rent, generally  attended  by  a  violent  contraction  of  the 
muscular  fibres. 

Short-Circuit. — A  shunt,  or  by-pass,  of  comparatively 
small  resistance,  around  the  poles  of  an  electric  source,  or 


WORDS,  TERMS  AND  PHRASES.  54T 

around  any  portion  of  a  circuit,  by  which  so  much  of  the  cur- 
rent passes  as  virtually  to  cut  out  any  other  circuit  connected 
therewith,  and  so  prevent  it  from  receiving  an  appreciable 
current. 
Short-Circuit  Key.— (See  Key,  Short  Circuit.) 

Mm  HI  Circuits,  Resistance  of (See  Cir- 
cuits, Shunt,  Resistance  of.) 

Shunt  Circuits,  Uses  of (See  Circuits, 

Shunt,  Uses  of.) 

Shunt  Dynamo.— A  dynamo  electric  machine  the  field 
magnet  coils  of  which  are  in  a  shunt  circuit  around  the  ex- 
ternal circuit  of  the  machine.  (See  Dynamo  Electric  Ma- 
chine, Shunt.) 

Shunt,  Electro-magnetic In  a  system  of  tele- 
graphic communication  an  electro  magnet  whose  coils  are 
placed  in  a  shunt  circuit  around  the  terminals  of  the  receiving 
relay. 

The  electro-magnetic  shunt  operates  by  its  self  induction. 
Its  poles  are  permanently  closed  by  a  soft  iron  armature,  so  as 
to  reduce  the  resistance  of  the  magnetic  circuit.  (See  Induction, 
Self.)  On  making  the  circuit  in  the  coils  of  the  receiving  relay, 
a  current  is  produced  in  the  coils  of  the  electro-magnetic  shunt 
in  the  opposite  direction  to  the  relay  current,  and,  on  breaking 
the  circuit  in  the  relay,  a  current  is  produced  in  the  coils  of 
the  electro-magnetic  shunt  in  the  same  direction  as  the  cur- 
rent in  the  receiving  relay.  The  connection  of  the  coils  of  the 
electro-magnetic  shunt  with  those  of  the  receiving  relay, 
however,  is  such  that  on  making  the  circuit  in  the  relay  the 
current  in  the  shunt  coils  flows  through  the  relay  in  the  same 
direction,  and  on  breaking  the  circuit  it  flows  in  the  opposite 
direction.  Therefore  this  shunt  effects  the  following  : 

(1)  At  the  commencement  of  each  signal  in  the  receiving 
relay,  it  produces  an  induced  current  in  the  same  direction 
which  strengthens  the  current  in  the 


548  A  DICTIONARY   OF  ELECTRICAL 

(2)  At  the  ending  of  each  signal  in  the  receiving  relay,  it 
produces  a  current  in  the  opposite  direction,  which  hastens 
the  motion  of  the  tongue  of  the  polarized  relay.  (See  Relay, 
Polarized.) 

Sim  11 1  for  Galvanometer.— (See  Galvanometer  Shunt.) 

Shunt  or  Derived  Circuit.— A  branch  or  additional 
circuit  provided  at  any  part  of  a  circuit,  through  which  the 
current  branches  or  divides,  part  flowing  through  the  original 
circuit,  and  part  through  the  new  branch. 

In  the  case'of  branched  circuits  each  of  the  circuits  acts  as 
a  shunt  to  the  others.  Any  number  of  additional  or  shunt 
circuits  may  be  thus  provided.  (See  Kirchhoff's  Laivs.) 

Shunt,  Magnetic An  additional  path  of  mag- 
netic material  provided  in  a  magnetic  circuit  for  the  passage 
of  the  lines  of  force. 

Shunts,  multiplying  Power  of A  quantity, 

by  which  the  current  flowing  through  a  galvanometer  pro- 
vided with  a  shunt,  must  be  multiplied,  in  order  to  give  the 
total  current. 

The  multiplying  power  of  a  shunt  may  be  determined  from 
the  following  formula,  viz. : 

A  =  fs+flrN)  X  C,  in  which  s~>r9  -  the  Multiplying   Power 

\.     s     /  & 

of  a  Shunt  whose  resistance  is  s ;  g,  is  the  galvanometer  resist- 
ance; C,  the  current  through  the  galvanometer;  and  A,  the 
total  current  passing  ;  s  and  g,  are  taken  in  ohms,  and  C  and 
A,  in  amperes. 

Suppose,  for  example  that  but  1/10  the  entire  current  is  to 
flow  through  the  galvanometer,  then  the  resistance  of  the 
shunt  must  evidently  be  £  g,  for, 

s  1  1 


s  +  g      1  +  9 
or,  10  s  =  s  +  gr.    10  s  —  s=g 


WORDS,  TERMS  AND  PHRASES.  549 

Sidero-Magiietic.— A  term  proposed  by  Sylvanus  P. 
Thompson  to  replace  the  word  ferro-magnetic. — (See  Ferro- 
Magnetic.) 

Siemens  and  Halskc  Voltaic  Cell.— (See  Cell,  Voltaic.) 

Signals,  Electro  Pneumatic Signals  operated 

by  the  movements  of  diaphragms  or  pistons  moved  by  com- 
pressed air,  the  escape  of  which  is  controlled  electrically. 

Signaling,  Telocity  of  Transmission  of 

The  speed  or  rate  at  which  successive  signals  can  be  sent  on  any 
line  without  the  retardation  producing  serious  interference. 
(See  Retardation  of  Signals.) 

Silurus  electricus.— The  electric  eel. — (See  Electric  Eel. 
Silver  Bath. — (See  Baths,  Silver,  etc.) 
Simple  Magnet.— (See  Magnet,  Simple.) 
Simple  Voltaic  Cell.— (See  Cell,  Voltaic.) 
Sine  Galvanometer.— (See  Galvanometer,  Sine.) 
Single  Fluid  Cell.— A  voltaic  cell  in  which  both  elements 
of  the  couple  are  immersed  in  the  same  electrolyte.     (See 
Cell,  Voltaic  Single  Fluid.) 

Single  Fluid  Electrical  Hypothesis.— A  hypothesis 
framed  to  explain  the  phenomena  of  electricity  on  the  as- 
sumption of  a  single  electric  fluid  possessed  by  all  matter. 
(See  Electricity,  Single  Fluid  Hypothesis  of.) 

Single  Touch.— A  method  of  magnetization  in  which  the 
magnetizing  bar  is  merely  drawn  from  one  end  to  the  other 
of  the  bar  to  be  magnetized,  and  returned  through  the  air  for 
the  next  stroke.    (See  Magnetization,  Methods  of.) 
Sinistrorsal  Solenoid.— (See  Solenoid,  Sinistrorsal) 
Sinuous  Currents.— (See  Currents,  Sinuous.) 
Siphon  Recorder. — (See  Recorder,  Siphon.) 
Skin,  Faradization  of —  —  The  therapeutic  treat- 

ment of  the  skin  by  a  faradic  current. 


550  A  DICTIONARY  OP  ELECTRICAL 

For  efficient  faradization  the  skin  should  be  thoroughly  dried 
and  a  metallic  brush  or  electrode  employed.  For  very  sensi- 
tive parts,  as,  for  example,  the  face,  the  hand  of  the  oper- 
ator, first  thoroughly  dried,  is  to  be  preferred  as  an  electrode. 

Skin,  Human,  Electric  Resistance  of 

The  electric  resistance  offered  by  the  skin  of  the  human  body. 

The  electric  resistance  of  the  skin  is  subject  to  marked  dif- 
ferences in  different  parts  of  the  body,  where  its  thickness  or 
continuity  varies.  It  varies  still  more  with  variations  in  its 
condition  of  moisture.  Even  in  the  same  individual  the 
resistance  varies  materially  under  apparently  similar  con- 
ditions. 

Sled. — The  sliding  contacts  drawn  after  a  moving  electric 
railway  car  through  the  slotted  underground  conduit  con- 
taining the  wires  or  conductors  from  which  the  driving  cur- 
rent is  taken. 

Slide  Balance,  Wheatstone's.— (See  Balance,  Wheat- 
stone's  Electric.} 

Smee's  Voltaic  Cell.— (See  Cell,  Voltaic.) 

Socket,  Electric  Lamp A  support  for  the  re- 
ception of  an  incandescent  electric  lamp. 

Incandescent  lamp  sockets  are  generally  made  so  that  the 
mere  insertion  of  the  base  of  the  lamp  in  the  socket  completes 
the  connection  of  the  lamp  terminals  with  terminals  of  the 
socket  connected  with  the  leads  that  supply  current  to  the 
lamp,  and  its  removal  from  the  socket,  automatically  breaks 
such  circuit.  The  socket  is  generally  provided  with  a  key  for 
turning  the  lamp  on  or  off  without  removing  it  from  the  socket. 

Figs.  347  and  348,  show  forms  of  lamp  sockets  for  incan- 
descent lamps  and  the  details  of  the  key  for  connecting  or  dis- 
connecting the  lamp  with  the  leads. 

Soldering,  Electric The  uniting  of  metals  to 

one  another,  in  which  heat  generaterd  by  the  electric  current 
is  used  to  melt  the  solder  in  the  place  of  ordinary  heat. 


WORDS,  TERMS  AND  PHRASES.  551 

(See  Solenoid  Prac- 


Soleiioid,  Dcxtrorsal  — 

tical) 

Solenoid,  Ideal  —A  solenoid  consisting  of  a 

cylinder  built  up  of  true  circular  currents,  with  all  their  faces 
of  like  polarity  turned  in  the  same  direction  and  entirely  in- 
dependent of  one  another. 

The  practical  solenoid  differs  from  the  ideal  solenoid  in  that 
the  successive  circular  circuits  or  currents  are  all  connected 
with  one  another  in  series. 


Fig.  3U7. 


Fig. 


Solenoid  or  Helix.    Electro-Magnetic  Solenoid. 

—The  name  given  to  a  cylindrical  coil  of  wire,  each  of  the 
convolutions  of  which  is  circular. 

A  circuit  bent  in  the  form  of  a  helix,  supported  at  its  two 
extremities,  as  shown  in  Fig.  349,  and  traversed  by  an  elec- 
tric current,  will  move  into  the  magnetic  meridian  of  the 
place,  and  if  free  to  move  in  a  vertical  plane,  will  come  to 
rest  in  the  line  of  the  dip  of  the  place. 

A  solenoid  traversed  by  an  electric  current  acquires  thereby 
all  the  properties  of  a  magnet,  and  is  attracted  and  repelled 
by  other  magnets.  Its  poles  are  situated  at  the  ends  of  the 
cylinder  on  which  the  solenoid  may  be  supposed  to  be  wound. 


552 


A  DICTIONARY  OF  ELECTRICAL 


The  polarity  of  a  solenoid  depends  on  the  direction  of  the 
current  as  regards  the  direction  in  which  the  solenoid  is 
wound. 

This  solenoid  is  sometimes  called  an  electro-magnetic 
solenoid  or  helix,  in  order  to  distinguish  it  from  a  mag- 
netic solenoid  or  solenoidal  magnet.  (See  Magnet,  Sole- 
noidal.) 

A  solenoid,  if  suspended  so  as  to  be  free  to  move,  will  come 
to  rest  in  the  plane  of  the  magnetic  meridian. 

It  will  also  be  attracted  or  repelled  by  the  approach  of  a 
dissimilar  or  similar  magnet  pole  respectively,  Fig.  351. 


Solenoid,   Practical 


Fig.  350. 


— The  name  applied  to 
the  ordinary  solenoid  in 
order  to  distinguish  it 
from  the  ideal  solenoid. 
(See  Solenoid,  Ideal. ) 

A  practical  solenoid 
consists,  as  shown  in 
Fig.  350,  of  a  spiral  coil 
of  wire  wrapped  in  the 
manner  shown  in  the 
figures  at  (1),  (2)  and  (3.) 

The  polarity  of  the 
solenoid  depends  on  the 
direction  of  the  current, 
and  therefore  on  the 
direction  of  winding. 
In  any  solenoid,  how- 
ever, the  polarity  may 
be  reversed  by  revers- 
ing the  direction  of  the 
current.  (See  Electro- 
Magnet.) 


A  Right  Handed,  or  Dextrorsal  Solenoid,  is  one  wound  in 
the  direction  shown  at  (1). 


WORDS,  TERMS  AND  PHRASES. 


A  Left  Handed,  or  Sinistrorsal  Solenoid,  is  one  wound  in 
the  direction  shown  at  (2). 

The  solenoid  shown  at  (3)  is  wound  so  as  to  produce  con- 
sequent poles.  (See  Consequent  Poles,  or  Points.) 


Solenoid,  Siiiistrorsal 

tical) 

Sonometer,    Hughes' 

balance  for  the  purpose 
of  examining  the  inten- 
sity of  sounds,  or  the  del- 
icacy of  the  ear  in  de- 
tecting or  distinguishing 
sounds.  (See  Induction 
Balance,  Hughes.} 

Sonoresce  nee 

A  term  proposed 

for  the  sounds  produced 
when  a  piece  of  vulcanite 
or  any  other  solid  sub- 
stance is  exposed  to  a 
rapid  succession  of  flashes 
of  light.  See  Photo- 
phone.) 

Sound  (Subjectively) 
The  effect  pro- 
duced by  a  vibrating 
body. 

Sound   (Objectively). 


— (See  Solenoid,  Prac- 


Fig.  351. 


The  waves  in  the  air  or  other  medium  which  produce  sound. 

The  word  sound  is  therefore  used  in  science  in  two  distinct 
senses,  viz.  : 

(1.)  Subjectively,  as  the  sensation  produced  by  the  vibration 
of  a  sonorous  body. 


554  A  DICTIONARY  OF  ELECTRICAL 

(2.)  Objectively,  as  the  waves  or  vibrations  that  are  cap- 
able of  producing  the  sensation  of  sound. 

Sound  is  transmitted  from  the  vibrating  body  to  the  ear  of 
the  hearer  by  means  of  alternate  to-and-fro  motions  in  the 
air,  occurring  in  every  direction  around  the  vibrating  body 
and  forming  spherical  waves  called  waves  of  condensation 
and  rarefaction.  Unlike  light  and  heat,  these  waves  require 
a  tangible  medium  such  as  air,  to  transmit  them. 

Sound,  therefore,  is  not  propagated  in  a  vacuum.  The  vibra- 
tions of  sound  are  longitudinal,  that  is,  the  to-and-fro  motions 
occur  in  the  same  direction  as  that  in  which  the  sound  is 
traveling.  The  vibrations  of  light  are  transverse,  that  is,  the 
to-and-fro  motions  are  at  right  angles  to  the  direction  in 
which  the  light  is  traveling. 

Sound,  Characteristics  of (See  Character- 
istics of  Sound.) 

Sounder,  Morse  Telegraphic —An 

electro-magnet  which  produces  audible  sounds  by  the  move- 
ments of  a  lever  attached  to  the  armature  of  the  magnet. 

The  Morse  sounder  has  now  almost  entirely  supplanted  the 
paper  recorder  or  register.  On  short  lines  it  is  placed  directly 
in  the  telegraphic  circuit.  On  long  lines  it  is  operated  by  a 
local  battery,  thrown  into  or  out  of  action  by  the  relay.  (See 
Relay.) 

The  Morse  sounder,  shown  in  Fig.  352,  consists  of  an  upright 
electro  magnet  M,  whose  soft  iron  armature  A  is  rigidly  at- 
tached to  the  striking  lever  B,  working  in  adjustable  screw 
pivots  as  shown.  The  free  end  of  the  lever  is  limited  in  its 
strokes  by  two  set  screws  N,  N.  The  lower  of  these  screws 
is  set  so  as  to  limit  the  approach  of  the  armature  A  to  the  poles 
of  the  electro  magnet ;  the  upper  screw  is  set  so  as  to  give  the 
end  B,  sufficient  play  to  produce  a  loud  sound.  A  retractile 
spring,  attached  to  the  striking  lever  near  its  pivoted  end,  and 
provided  with  regulating  screw  S  S,  pulls  the  lever  back  when 
the  current  ceases  to  flow  through  M. 


WJBDS,  TEKMS    ANU    PHKASSttS.  555 

The  dots  and  dashes  of  the  Morse  alphabet  are  reproduced 
by  the  sounder,  as  audible  signals,  that  are  distinguished  by 
the  operator  by  means  of  the  different  sounds  produced  by  the 
up  and  down  stroke  of  the  lever  as  well  as  by  the  difference 
in  the  intervals  of  time  between  the  successive  signals. 

Sounds,  magnetic (See  Magnetic  Sounds.) 

Source,  Electric.— Anything  which  produces  a  difference 
Of  potential  or  an  electro-motive  force. 
Spark  Discharge.— (See  Discharge,  Disruptive.) 

Spark,  Length  of —  (See  Length  of  Spark.) 

JV 


Fig.  352. 

Spark  Tube.— A  high  vacuum  tube,  across  which  the 
spark  from  an  induction  coil  will  not  pass,  when  the  vacuum 
is  sufficiently  high. 

A  spark  tube,  connected  with  incandescent  lamps  which 
are  undergoing  exhaustion,  acts  as  a  simple  gauge  to  deter- 
mine the  degree  of  exhaustion.  When  an  induction  coil  dis- 
charge ceases  to  pass,  or  to  freely  pass,  the  vacuum  is  con- 
sidered as  sufficient,  according  to  circumstances. 

Sparking  of  Dynamo-Electric  Machines. — An  ir- 
regular and  injurious  action  at  the  commutator  of  a  dynamo. 


556  A  DICTIONARY  OF  ELECTRICAL 

electric  machine,  attended  with  spark  at  the  collecting 
brushes. 

Sparking  consists  in  the  formation  of  small  arcs  under  the 
collecting  brushes.  One  cause  of  sparking  is  to  be  found  in 
the  brushes  leaving  one  commutator  strip  before  making  con- 
nection with  the  next  strip.  Sparking  causes  a  burning  of  the 
commutator  strips,  and  an  irregular  consumption  of  the 
brushes,  both  of  which  produce  further  irregularities  by  wear 
or  friction  of  the  brushes  against  the  commutator  bars. 
Sparking  from  this  cause  may  be  avoided  by  so  placing  the 
brush  as  to  cause  it  to  bridge  over  the  space  between  two 
consecutive-bars,  thus  permitting  it  to  touch  one  bar  before 
leaving  the  other.  Two  brushes,  electrically  connected,  are 
sometimes  employed  for  this  purpose,  or  the  slots  between 
contiguous  bars  are  slightly  inclined  to  the  axis  of  rotation. 

At  the  moment  the  brush  touches  two  contiguous  commuta- 
tor bars,  it  short  circuits  the  coil  terminating  at  those  bars. 
On  the  breaking  of  this  closed  circuit,  a  spark  appears  under 
the  brushes.  This  spark  is  often  considerable,  since  from  the 
comparatively  small  resistance  of  the  coil,  it  is  apt,  when 
short-circuited  to  produce  a  heavy  current. 

Another  cause  of  sparking  is  to  be  found  in  the  self-induc- 
tion of  the  armature  coils.  The  extra  current  on  breaking 
forms  an  injurious  spark  under  the  brushes.  This  spark  may 
be  considerable  since  the  current  produced  in  the  coil  on  mo- 
mentarily short-circuiting  it  by  the  brushes  simultaneously 
touching  the  adjoining  commutator  segments  may  be  large. 

Sparking  occurs  when  the  brushes  are  not  set  close  to  the 
neutral  line.  Since  the  principal  cause  for  this  change  in  the 
lead  of  the  brushes  is  the  magnetizing  effect  of  the  armature 
coils,  it  is  preferable  to  make  the  number  of  windings  of  these 
as  few  as  possible  and  to  obtain  the  necessary  differences  of 
potential  by  increasing  the  speed  of  rotation  and  the  strength 
of  the  magnetic  field  of  the  machine.  Short  armature  coils 
also  lessen  the  sparking  due  to  self-induction. 


WORDS,  TERMS  AND  PHRASES,  557 

Sparking  at  the  brushes  is  also  caused  by  the  jumping  of 
improperly  supported  or  constructed  brushes. 

When  the  brushes  are  not  set  close  to  the  neutral  point  long 
flashing  sparks  are  apt  to  occur. 

A  lack  of  symmetry  of  winding  of  the  armature  coils  will 
necessarily  be  attended  by  injurious  flashing,  from  the  impos- 
sibility of  properly  adjusting  the  brushes. 

Specific  Heat.— (See  Heat,  Specific.) 

Specific  Heat  of  Electricity.— A  term  proposed  by  Sir 
Wm.  Thomson  to  indicate  the  analogies  between  the  absorp- 
tion and  emisssion  of  heat  in  purely  thermal  phenomena,  and 
the  absorption  and  emission  of  heat  in  thermo  electric  phe- 
nomena. 

As  we  have  already  seen  heat  is  either  given  out  or  absorbed, 
when  an  electric  current  passes  from  one  metal  to  another 
across  a  junction  between  them.  (See  Effect,  Peltier.) 

Co,  too,  when  electricity  passes  through  an  unequally  heated 
wire  the  current  tends  to  increase  or  decrease  the  differences 
of  temperature,  according  to  the  direction  in  which  it  flows, 
and  according  to  the  character  of  the  metal.  (See  Effect, 
Thomson.) 

"If  electricity  were  a  fluid,"  says  Maxwell,  "running 
through  the  conductor  as  water  does  through  a  tube,  and 
always  giving  out  or  absorbing  heat  till  its  temperature  is 
that  of  the  conductor,  then  in  passing  from  hot  to  cold  it  would 
give  out  heat,  and  in  passing  from  cold  to  hot  it  would  absorb 
heat,  and  the  amount  of  this  heat  would  depend  on  the  spe- 
cific heat  of  the  fluid." 

Specific  Inductive  Capacity  .—(See  Capacity,  Specific 
Inductive.) 

Specific  Resistance.— (See  Resistance,  Specific.) 
Specific  Resistance  of  Liquids.— (See  Liquids,  Spe- 
cific Resistance  of.) 
Speech,  Articulate. (See  Articulate  Speech.) 


558  A  DICTIONARY  OF  ELECTRICAL 

Sphygmograph.— An  electric  apparatus  for  obtaining  a 
record  of  the  rate  and  strength  of  the  pulse. 

Sphygmophone. — An  applicatoin  of  the  microphone 
to  the  medical  examination  of  the  pulse.  (See  Microphone.) 

Spiral,  RogCt's A  suspended  wire  spiral  convey- 
ing a  strong  electric  current,  and  devised  to  show  the  attrac- 
tions produced  by  parallel  currents  flowing  in  the  same  direc- 
tion. 

The  lower  end  of  the  wire  spiral  dips  into  a  mercury  cup. 
On  the  passage  of  the  current,  the  attraction  of  the  neighboring 
turns  of  the  spiral  for  each  other  shortens  the  length  of  the 
spiral  sufficiently  to  draw  it  out  of  the  mercury  and  thus  break 
the  circuit.  When  this  occurs  the  weight  of  the  spiral  causes 
it  to  fall  and  again  re-establish  the  circuit.  A  rapid  automatic 
make-and-break  is  thus  established,  accompanied  by  a  bril- 
liant spark  at  the  mercury  surface  due  to  the  extra  spark  on 
breaking. 

Split  Battery.— (See  Battery,  Split.) 

Spring- Jack.— A  device  for  readily  inserting  a  loop  in  a 
main  electric  circuit.  (See  Board,  Multiple  Switch.) 

Spring- Jack  Cut-Oat,— A  device  similar  in  general  con- 
struction to  a  spring  jack,  but  employed  to  cut  out  a  circuit. 

An  insulated  plug  is  thrust  between  spring  contacts,  thus 
breaking  the  circuit  by  forcing  them  apart. 

Spurious  Resistance. — A  false  resistance  arising  from 
the  development  of  a  counter  electro-motive  force.  (See 
Counter  Electro-Motive  Force.) 

Standard  Candle.— (See  Candle,  Standard.) 

Standard  Carcel  Gas  Jet.— (See  Carcel  Standard  Gas 
Jet.) 

Standard  Cell.— A  voltaic  cell  the  electro-motive  force 
of  which  is  constant,  and  which,  therefore,  may  be  used  in  the 
measurement  of  an  unknown  electro-motive  force. 


WORDS,  TERMS  AND  PHRASES. 


559 


Absolute  constancy  is  impossible  to  attain,  but,  if  the  current 
of  the  standard  cell  is  closed  but  for  a  short  time  the  electro- 
motive force  may  be  regarded  as  invariable. 

Standard  Cell,  Clark's  —  —The  form  of  standard 
cell  shown  in  Fig.  353. 

Latimer  Clark's  Standard  Cell,  assumes  a  variety  of  forms, 
The  H-form  is  arranged  as  shown  in  Fig.  353.  The  vessei 
to  the  left  contains  at  A  an  amalgam 
of  pure  zinc.  The  other  vessel  contains 
at  M  mercury  covered  with  pure  mer- 
curous  sulphate.  Both  vessels  are  then 
filled  above  the  level  of  the  cross  tube, 
with  a  saturated  solution  of  zinc  sul- 
phate Z,  Z,  to  which  a  few  crystals  of 
the  same  are  added.  Tightly  fitting 
corks  C,  C,  prevent  loss  by  evaporation. 

The  value  of  this  cell  in  legal  volts  is 
1.438 (1  —  0.00077  (t  —  15°  C.)    (Ayrton.) 

The  value  t,   is  the  temperature  in 
degrees  of  the  centigrade  scale. 

Standard     Cell,     Fleming's 


Fig.  353. 
—The  form  of  standard  cell  shown  in  Fig.   354. 


The  U  tube,  Fig.  354,  is  connected,  as  shown,  by  means  of 
taps,  with  two  vessels  filled  with  chemically  pure  solutions 
of  copper  sulphate  of  Sp.  Gr.  1.1  at  15°  C.,  and  zinc  sulphate 
of  Sp.  Gr.  1.4  at  15°  C.  respectively.  To  use  the  cell  the  zinc 
rod  Zn,  connected  with  a  wire  passing  through  a  rubber 
stopper  is  placed  in  the  left  hand  branch.  The  tap  A  is  opened 
and  the  entire  U-tube  is  filled  with  the  denser  zinc  sul- 
phate solution.  The  tap  at  C  is  then  opened,  and  the 
liquid  in  the  right  hand  branch  above  the  tap  is  discharged 
into  the  lower  vessel,  but,  from  this  part  only.  The 
tap  C  is  then  closed,  and  the  tap  B  opened,  and  the  lighter 
copper  sulphate  allowed  to  fill  the  right  hand  branch  above  the 
tap  C.  The  copper  rod  CM,  fitted  to  a  rubber  stopper  and  con- 


560 


A  DICTIONARY  OF  ELECTRICAL 


nected  with  a  conducting  wire,  is  then  placed  in  the  copper 

solution. 
Tubes  are  provided  at  L  and  M,  for  the  reception  of  the  zinc 

and  copper  tubes  when  not  in  use.  The  copper  tube  is 
prepared  for  use  by  freshly  elec- 
tro-plating it  with  copper.  The 
E.  M.  F.  of  this  cell  is  1.074 
volts.  If  the  line  of  demar- 
cation between  the  two  liquids 
is  not  sharp,  the  arms  of  the 
vessels  are  emptied,  and  fresh 
liquid  is  run  in. 

Standard  Resistance 

Coil.— (See  Resistance     Coil, 
Standard.) 
State,    Allotropie  

— (See  Allotropy.) 

State,   Nascent 

(See  Nascent  State.) 

State,    Passive  of 

Iron. — (See  Passive  State.) 
State,  Permanent 

The  condition  of  the  charge 
of  a  telegraph  wire  when  the 
current  reaching  the  distant  end 

has  the  same  strength  as  at  the 

Fig.  35U.  sending  end. 

State,  Variable The  condition  of  the  charge  of 


a  telegraph  wire  while  the  strength  of  current  is  increasing 
up  to  the  full  strength  in  all  parts. 

The  duration  of  the  variable  state  is  directly  as  the  length 
of  the  line  and  its  total  resistance.  It  is  increased  by  leakage, 
and  by  the  effect  of  the  extra  current.  (See  Currents,  Ex- 
tra.) 


WORDS,  TERMS  AND  PHRASES.  561 

Static  Charge. — (See  Charge,  Static.) 

Static  Electricity.— A  term  formerly  applied  to  electri- 
city produced  by  friction.  (Now  obsolete.) 

The  term  static  electricity  is  properly  employed  in  the  sense 
of  a  static  charge  but  not  as  static  electricity,  since  that  would 
indicate  a  particular  kind  of  electricity,  and,  as  is  now  gen- 
erally recognized,  electricity,  from  no  matter  what  source  it 
is  derived,  is  one  and  the  same  thing. 

Statics.— The  science  which  treats  of  the  relations  that 
must  exist  between  the  points  of  application  of  forces  and 
their  direction  and  intensity,  in  order  that  equilibrium  may 
result. 

Stay  Rods,  Telegraphic Metallic  rods, 

attached  to  a  telegraph  pole,  and  securely  fastened  in  the 
ground  in  order  to  counteract  the  effects  of  a  pull  or  tension 
on  the  poles.  (See  Poles,  Telegraphic.) 

Steel,  qualities  of Requisite  for  Magnetiza- 
tion.— Qualities  which  must  be  possessed  by  steel  in  order  to 
permit  it  to  permanently  retain  a  considerable  magnetization. 

For  the  purposes  of  magnetization  steel  should  possess  the 
following  qualities; 

It  should  be  hard,  and  fine  grained.  Hard  cast  steel  answers 
the  purpose  very  well.  Scoresby  showed  that  an  intimate 
relation  exists  between  the  quality  of  the  iron  from  which  the 
steel  is  made,  and  its  ability  to  take  and  retain  considerable 
magnetism. 

An  admixture  to  steel  of  about  .03  per  cent,  of  tungsten 
is  said  to  increase  its  magnetic  powers.  Cast  steel  is  not 
generally  employed  for  magnets,  wrought  steel  being  gen- 
erally preferred. 

St.  Elmo's  Fire.— Faintly  luminous  globes,  due  to  elec- 
tric brush  discharges,  sometimes  seen  on  the  ends  of  a  ship's 
masts,  or  other  similar  locations. 


562 


A  DICTIONARY  OF  ELECTRICAL 


Step-foy-Step  or  Dial  Telegraphy.— A  system  of 
telegraphy  in  which  the  signals  are  registered  by  the  move- 
ments of  a  needle  over  a  dial  on  which  the  letters  of  the  alpha- 
bet, etc.,  are  marked. 

Dial  telegraphs  are  employed  for  communication  by  those 
who  are  unable  to  readily  read  the  Morse  characters. 

The  annexed  instrument,  devised  by  Breguet,  was  formerly 
used  on  some  of  the  railway  systems  of  France. 


Fig.  355. 


Fig.  356. 


A  needle  advances  over  a  dial  in  one  direction  only  by  a  step- 
by-step  movement.  The  alternate  to-and-fro  motions  of  the 
armature  of  an  electro  magnet  are  employed  to  impart  a  step- 
by-step  motion  to  a  peculiarly  shaped  toothed  wheel  T,  T,  Fig. 
355,  through  the  action  of  a  horizontal  arm  c,  attached  there- 
to, and  moving  between  the  two  prongs  of  a  fork  d,  vibrating 
on  a  horizontal  axis  to  which  is  attached  a  vertical  pallet  i. 

The  receiving  instrument  is  called  the  Indicator,  and  con- 
sists of  a  needle  attached  to  the  axis  of  this  wheel.  The 
needle  moves  over  the  face  of  the  dial ,  shown  in  the  Fig.  356, 
on  which  are  marked  the  letters  of  the  alohabet  and  the  nu- 
merals. 

The  sending  instrument  is  called  the  Manipulator.     It  con- 


WORDS,  TERMS  AND  PHRASES. 


563 


sists  of  a  device  for  readily  sending1  over  the  line  the  number 
of  successive  impulses  required  to  move  the  needle  step-by- 
step  from  any  letter  on  the  indicator  ,to  which  it  may  be  point- 
ing1, to  the  next  it  is  desired  to  send.  The  dial,  shown  in  Fig. 
357,  is  marked  on  its  face  with  the  same  characters  as  the  in- 
dicator. The  edge  oi  the  wheel  is  provided  with  twenty-six 
notches  in  which  a  pin  attached  to  a  movable  arm  engages. 
This  arm  is  jointed  so  that  it  can  be  placed  in  any  of  the 
notches  on  the  face  of  the  wheel. 


FliJ.  357. 

Below  the  dial  face,  and  attached  to  the  same  axis  as  the 
movable  arm,  is  a  wheel  provided  with  undulations  consisting 
of  thirteen  elevations  and  thirteen  depressions. 

A  lever  T,  pivoted  at  a,  rests  in  these  undulations  at  its 
upper  end,  and  plays  between  two  contact  points  at  P  and  Q. 

If,  now.  the  dials  of  the  indicator  and  the  manipulator  both 
being  at  o,  a  movement  is  given  to  the  arm  by  the  handle  M, 


564  A  DICTIONARY   OF  ELECTRICAL 

to  any  point  on  the  manipulator,  there  are  thus  produced  the 
required  number  of  makes  and  breaks  to  move  the  needle  of 
the  indicator  to  the  corresponding1  letter  or  character. 

Step-foy-Step  Telegraphy.— (See  Telegraphy,  Step-by- 
Step.) 

Stool,  Insulating.— A  stool,  provided  with  insulating 
supports  of  vulcanite  or  other  insulator,  employed  to  afford  a 
ready  insulating  stand  or  support.  (See  Insulating  Stool.) 

Storage  Cell§,  or  Accumulators.— Two  inert  plates 
of  metal,  or  of  metallic  oxides,  immersed  in  an  electrolyte  in- 
capable of  acting  on  them  until  after  an  electric  current  has 
been  passed  through  the  liquid  from  one  plate  to  the  other. 

On  the  passage  of  an  electric  current  through  the  electro- 
lyte, its  decomposition  is  effected  and  the  electro  positive  and 
electro  negative  radicals  are  deposited  on  the  plates,  or  unite 
with  them,  so  that  on  the  cessation  of  the  charging  current, 
there  remains  a  voltaic  cell  capable  of  generating  an  electric 
current. 

A  storage  cell  is  charged  by  the  passage  through  the  liquid 
from  one  plate  to  the  other  of  an  electric  current,  derived 
from  any  external  source.  The  charging  current  produces  an 
electrolytic  decomposition  of  the  inert  liquid  between  the 
plates,  depositing  the  electro  positive  radicals,  or  kathions,  on 
the  plate  connected  with  the  negative  terminal  of  the  source, 
and  the  electro  negative  radicals,  or  anions,  on  the  plate  con- 
nected with  the  positive  terminal. 

On  the  cessation  of  the  charging  current,  and  the  connec- 
tion of  the  charged  plates  by  a  conductor  outside  the  liquic 
a  current  is  produced,  which  flows  through  the  liquid  from 
the  plate  covered  with  the  electro  positive  radical,  to  that 
covered  with  the  electro  negative  radical,  or  in  the  opposite 
direction  to  that  of  the  charging  current. 

The  simplest  storage  cell  is  Plante's  cell,  which,  as  origin- 
ally constructed,  consists  of  two  plates  of  lead  immersed  in 
dilute  sulphuric  acid,  H8  SO4.  On  the  passage  of  the  char:;- 


WORDS,  TERMS  AND  PHRASES. 


565 


ing  current,  the  plates  A  and  B,  Fig.  358.  dipped  in  Hz  SO4, 
are  covered  respectively  with  lead  peroxide  Pb  O2,  and  finely 
divided,  spongy  lead.  The  peroxide  is  formed  on  the  positive 
plate,  and  the  metallic  lead  on  the  negative  plate. 

When  the  charging  current  ceases  to  pass,  the  cell  dis- 
charges m  the  opposite  direction,  viz.,  from  B'  to  A',  that  is, 
from  the  spongy  lead  plate  to  the  peroxide  plate,  as  shown  in 
Fig.  359. 


1HHH 


Fig.  358. 


Discharging 
Fig.  359. 


As  a  result  of  this  discharging  current  the  peroxide,  Pb  Ot, 
on  A',  gives  up  one  of  its  atoms  of  oxygen  to  the  spongy  lead 
on  B',  thus  leaving  both  plates  coated  with  a  layer  of  Pb  O, 
lead  monoxide,  or  litharge.  When  this  change  is  thoroughly 
effected,  the  cell  becomes  inert,  and  will  furnish  no  further 
current  until  again  charged  by  the  passage  of  a  current  from 
some  external  source. 

In  order  to  increase  the  capacity  of  the  storage  cells,  and  thus 
prolong  the  time  of  their  discharge,  the  coating  of  lead 
monoxide  thus  left  on  each  of  the  plates,  when  neutral,  is 
made  as  great  as  possible.  To  effect  this,  a  process  called 
forming  the  plates  is  employed,  which  consists  in  first  charg- 
ing the  plates  as  already  described,  and  then  reversing  the 


566  A  DICTIONARY   OF  ELECTRICAL 

direction  of  the  charging  current,  the  currents  being  sent 
through  the  cell  in  alternately  opposite  directions,  until  a  con- 
siderable depth  of  the  lead  plates  has  been  acted  on. 

It  will  be  noticed  that  during  the  action  of  the  charging 
current,  the  oxygen  is  transferred  from  the  PbOs,  on  one  plate, 
to  the  Pb  O.  on  the  other  plate,  thus  leaving  one  Pb,  and  the 
other  Pb  O8  ;  and  that  on  discharging,  one  atom  of  oxygen 
is  transferred  from  the  Pb  O2,  to  the  Pb,  thus  leaving  both 
plates  covered  with  Pb  O.  In  reality  this  is  but  the  final  result 
of  the  action,  4iydrated  sulphate  of  lead,  PbO,  Ha  SO4,  being 
formed,  and  subsequently  decomposed. 

In  order  to  decrease  the  time  required  for  forming,  accu- 
mulators or  secondary  cells  have  been  constructed,  in  which 
metallic  plates  covered  with  red  lead  Pbs  O4,  replace  the 
lead  plates  in  the  original  Plant6  cell.  On  charging,  the  Pbs 
O4,  is  peroxidized  at  the  anode,  i.  e.,  converted  into  Pb  O8,  and 
deoxidized,  and  subsequently  converted  into  metallic  lead  at 
the  kathode.  Or,  in  place  of  the  above  Pb3  O4,  red  lead  was 
placed  on  the  anode  and  Pb  O,  or  litharge  on  the  kathode. 

Plates  of  compressed  litharge  have  also  been  recently  used 
for  this  purpose.  Storage  cells  so  formed  have  a  greater  stor- 
age capacity  per  unit  weight  than  those  in  which  a  grid  is 
employed. 

In  all  such  cases,  various  irregularities  of  surface  are  given  to 
the  plates,  in  order  to  increase  their  extent  of  surface  and  to 
afford  a  means  for  preventing  the  separation  of  the  coatings. 
The  metallic  form  thus  provided  is  known  technically  as  a  grid. 

Unless  care  is  exercised,  the  plates  will  buckle  from  the  dif- 
ference in  the  expansion  of  the  lead  and  its  filling  of  oxide. 
This  buckling  is  attended  with  an  increase  in  the  resistance  of 
the  cell  and  the  gradual  separation  of  the  oxides  that  cover 
or  fill  it. 

Storage  of  Electricity. — A  term  improperly  employed 
to  indicate  such  a  storage  of  energy  as  will  enable  it  to  directly 
reproduce  electric  energy. 


WORDS,  TERMS  AND  PHRASES.  567 

A  so-called  storage  battery  does  not  store  electricity,  any 
more  than  the  spring  of  a  clock  can  be  said  to  store  time  or 
sound.  The  spring  stores  muscular  energy,  i.  e.,  renders  the 
muscular  kinetic  energy,  potential,  which,  again  becoming 
kinetic,  causes  the  works  of  the  clock  to  move  and  strike. 

In  the  same  way  in  a  so-called  storage  battery,  the  energy 
of  an  electric  current  is  caused  to  produce  electrolytic  decom- 
positions of  such  a  nature  as  to  independently  produce  a  cur- 
rent on  the  removal  of  the  electrolyzing  current.  (See  Stor- 
age Cells.) 

Storms,  Electric  or  magnetic (See  Magnetic 

Storms.") 

Storms.  Thunder  Geographical  Distribu- 
tion of.— The  following  general  facts  as  to  the  geographi- 
cal distribution  of  thunder  storms,  show  the  intimate  relation 
between  the  frequency  of  thunder  storms  and  the  time  and 
place  of  the  condensation  of  vapor. 

(1)  Thunder  storms  seldom,   if  ever,   occur  in  the  polar 
regions.     This  is  probably  because  the  rain  fall  here  results 
from  the  condensation  of  the  vapor  at  times  and  in  regions 
remote  from  the  times  and  regions  in  which  it  was  formed. 

(2)  Thunder  storms  seldom,  if  ever,  occur  in  rainless  districts 
owing  probably  to  the  absence  of  the  condensation  of  vapor. 

(3)  Thunder  storms  are  most  frequent  and  violent  in  the 
equatorial  regions,  where  the  rain  fall  results  from  the  con- 
densation of  the  vapor  by  the  action  of  ascending  currents, 
conveying  the  vapor  almost  immediately  after  its  formation 
into  the  upper  and  colder  regions  of  the  atmosphere. 

(4)  Thunder  storms  occur  in  regions  beyond  the  tropics,  at 
those  seasons  of  the  year  when  the  rain  fall  results  from  the 
condensation  of  the  vapor  shortly  after  the  time  of  its  for- 
mation, viz. ,  in  the  temperate  zones  in  the  hotter  parts  of  the 
year. 

Strain.— The  deformation  of  a  body  under  the  influence  of 
a  stress.  (See  Stress.) 


568  A  DICTIONARY   OF  ELECTRICAL 

Strain,  Dielectric (See  Dielectric  Strain.) 

Strain,    Electro  -  magnetic,    Optical (See 

Optical  Strain,  Electro-Magnetic.) 

Strain,  Electrostatic,  Optical  — See    Optical 

Strain,  Electrostatic.) 

Strain,  Optical (See  Optical  Strain.) 

Stratification  Tube.— An  exhausted  glass  tube,  the 
residual  atmosphere  of  which  displays  alternate  dark  and 
light  stria?,  or  stratifications,  on  the  passage  through  it  of 
an  induction  coil  discharge.  (See  Luminous  Effects  of  Dis- 
charge. ) 

Stray  Power. — A  term  used  to  indicate  the  power  lost  in 
driving  a  dynamo-electric    machine,    through    friction,   air 
churning  or  currents,  and  eddy  currents. 
Strength  of  Current.— (See  Current,  Strength.) 
Strength  of  Magnetism.— (See  Magnetism,  Intensity 
of.) 

Stres§. — The  pressure  or  pull  producing  a  deformation  or 
strain.  (See  Strain.) 

Stress,  Electrostatic,  or  Electro-magnetic  — 
— (See  Optical  Strain.) 

Striae.  Electric (See  Stratification  Tubes.) 

Struts  for  Telegraphic  Poles.— Inclined  wooden  or 

iron  poles,  applied  to  telegraph  poles  in  order  to  remove  the 

thrust  or  pressure  acting  on  them.     (See  Poles,  Telegraphic.) 

Sturgeon's    Wheel.— (See    Accumulator.    Barlow's 

Wheel.) 

Submarine  Boats.— (See  Boats,  Submarine.) 
Submarine  Cables. — (See  Cables,  Submarine.) 
Submarine  Mines. — (See  Mines,  Submarine.) 

Submarine  Telegraphy (See  Telegraphy, 

Systems  of. ) 


WORDS,  TERMS  AND  PHRASES.  569 

Substance,  Ferro-Magnetic.  —  (See  F err o- Magnetic 
Substance. 

Subway,  Electric An  accessible  underground 

way  or  passage  provided  for  the  reception  of  electric  wires 
or  cables. 

Underground  electric  conductors  like  all  electric  conduc- 
tors are  liable  to  faults,  crosses,  etc.,  etc.  Unless  they  are 
readily  accessible  very  serious  loss  and  damage  may  occur 
before  the  fault  is  located  and  corrected. 

Sun  Spots. — Dark  spots,  varying  in  number  and  position, 
which  appear  on  the  face  of  the  sun,  and  are  believed  to  be 
caused  by  huge  vortex  motions  in  the  masses  of  glowing  gas 
that  surround  the  sun's  body. 

Sun  spots  occur  in  greater  number  at  intervals  of  about 
every  eleven  years. 

Their  occurrence  is  generally  attended  with  unusual  terres- 
trial magnetic  variations.  (See  Magnetic  Storms.) 

Sunstroke,  Electric or  Electric  Pro§tra- 

liou,  or  Insolation.— Physiological  effects,  similar  to  those 
produced  by  exposure  to  the  sun,  experienced  by  those  ex- 
posed for  a  long-  while  to  the  intense  light  and  heat  of  the 
voltaic  arc. 

These  effects  were  first  noticed  by  Desprez  in  his  classic  ex- 
periments on  the  fusion  or  volatilization  of  carbon.  The  eyes 
are  irritated  and  the  skin  burned  as  by  the  sun.  In  some  cases 
it  is  claimed  that  the  effects  of  sunstroke,  or  excessive  produc- 
tion of  heat,  as  in  true  insolation,  are  produced.  In  the  more 
modern  application  of  electricity  to  electric  furnaces,  these 
same  effects  have  been  noticed  in  an  intensified  degree. 

From  some  recent  investigations  it  would  appear  that  these 
effects  are  to  be  ascribed  to  the  light  rather  than  to  the  heat. 

The  symptoms  are  as  follows  :  Pain  in  the  throat,  face  and 
temples,  followed  by  a  coppery  red  color  of  the  skin,  irritation 
and  watering  of  the  eyes,  when  the  symptoms  disappear. 
The  skin  peels  off  in  about  five  days. 


570  A  DICTIONARY  OF  ELECTRICAL 

Surfaces,  Equipotential  Electrostatic 

(See  Equipotential  Surfaces,  Electrostatic.) 

Surfaces,  Equipotential  Magnetic (See 

Equipotential  Surfaces,  Magnetic.) 

Susceptibility,  Magnetic A  term  ex- 
pressing the  ratio  existing  between  the  intensity  of  the 
induced  and  the  inducing  magnetism. 

The  magnetic  susceptibility  of  a  bar  of  iron  is  equal  to  the 
intensity  of  the  induced  magnetism  divided  by  the  strength 
the  inducing  field. 

Suspension,  Hi-Filar The  suspension  of  a 

needle  by  two  parallel  wires  or  fibres,  as  distinguished  from  a 
suspension  by  a  single  wire  or  fibre.  (See  Bi-Filar  Suspen- 
sion.) 

Suspension,  Combined  Fibre  and  Spring 

— The  suspension  of  a  needle  by  the  combined  use  of  a  spiral 
spring  and  a  single  fibre. 

In  this  form  of  suspension  the  spring  is  introduced  between 
the  fibre  and  the  needle.  It  is  valuable  for  marine  galvano- 
meters, and  other  apparatus  exposed  to  tilting  or  rolling 
motions,  because  it  permits  the  instrument  to  be  tilted 
through  several  degrees  without  causing  any  considerable 
variation  in  the  deflections  produced  by  the  current  or  the 
charge. 

Suspension,  Fibre Suspension  of  a  needle  by 

means  of  a  fibre  of  unspun  silk  or  other  material. 

A  fibre  suspension  generally  means  a  single  fibre  or  thread. 
It  may,  however,  be  applied  to  a  bi-filar  suspension.  (See 
Suspension,  Bi-Filar.) 

A  fibre  suspension  is  to  be  preferred  to  a  pivot  suspension, 
since  it  introduces  far  less  friction.  It  has,  however,  the  dis- 
advantage of  necessitating  levelling  screws. 

Suspension,  Knife  Edge The  suspension 


WORDS,  TERMS  AND  PHRASES. 


571 


of  a  needle  on  knife  edges  that  are  supported  on  steel  or  agate 
planes. 

A  suspension  of  this  kind  is  used  in  the  dipping  needle,  since 
it  permits  of  freedom  of  motion  in  a  single  vertical  plane  only. 

Suspension,  Pivot Suspension  of  a  needle 

by  means  of  a  jewelled  cup  and  a  metallic  pivot. 

The  jewelled  cup  is  placed  above  the  centre  of  gravity  of  the 
needle,  and  is  supported  on  a  steel  point.  As  a  rule  compass 
needles  have  this  variety  of  support. 


Fig. 


Switch,  Automatic  Telephone A  device  for 

transferring  the  connection  of  the  main  line  from  the  call 
bell  to  the  telephone  circuit. 

In  most  telephone  circuits,  as  now  arranged,  the  automatic 
switch,  beside  transfering  the  main  line  from  the  call  bell  to 
the  telephone  circuit,  closes  the  local  battery  circuit  of  the 
transmitter  on  the  removal  of  the  telephone  from  its  support- 
ing hook. 

The  means  whereby  this  is  accomplished  are  shown  in  Fig. 
360.  On  the  removal  of  the  telephone  from  the  hook  L, 
the  lever  is  pulled  upwards  by  the  spring  Z,  thus  closing  the 


572  A  DICTIONARY   OF  ELECTRICAL 

contacts  1,  2  and  3,  by  which  the  local  battery  S  is  closed  in 
the  circuit  of  the  transmitter,  the  telephone  disconnected 
from  the  circuit  of  the  call  bell  M,  B,  and  connected  with  the 
circuit  of  the  transmitter.  On  replacing  the  telephone  on  the 
hook  L  its  weight  depresses  the  lever,  breaking  connection 
with  1,  2  and  3,  and  establishing  connection  with  the  call  cir- 
cuit. 
Switch  Board.— (See  Board,  Switch.) 

Switch,  Double  Pole A  switch  that  makes  or 

breaks  contact  with  both  poles  of  the  circuit  in  which  it  is 
placed. 

Double-pole  switches  are  used  in  most  systems  of  incan- 
descent  lighting  in  order 
to  insure  the  thorough  sep- 
aration of  the  circuit  from 
the  main  conductor  or 
leads  when  cut  out. 
S  w  i  t  c  h,  Reversing 

A  switch  for 

reversing  the  direction  of 
the  battery   current 
Fig.  361.  through  a  galvanometer. 

A  simple  reversing  switch  consists  of  four  insulated  brass 
segments  mounted  on  a  plate  of  ebonite  and  furnished  with 
openings  between  them  for  plug  connections.  The  battery 
terminals  are  connected  to  two  diagonally  opposite  segments 
as  B  and  D,  Fig.  361,  and  the  leading  wires  of  the  galvanometer, 
or  other  instrument,  to  the  other  segments  as  C  and  A.  If  now 
the  plugs  are  placed  between  B  and  C,  and  A  and  D,  the 
battery  current  flows  in  one  direction.  If,  however,  the  plugs 
are  placed  between  A  and  B,  and  C  and  D,  the  battery  cur- 
rent will  flow  in  the  opposite  direction. 

The  battery  current  is  cut  oif  if  one  plug  is  removed.  In 
practice,  however,  it  is  perferable  to  remove  both  plugs,  so  as 
to  avoid  any  current  from  want  of  sufficienc  insulation. 


WORDS,  TERMS  AND  PHRASES.  573 

Sympathetic  Vibrations.— Vibrations  set  up  in  bodies 
by  sound  waves  of  exactly  the  same  wave  length  as  those 
produced  by  the  vibrating1  body. 

The  pitch  or  tone  of  the  note  produced  by  the  body  set  into 
sympathetic  vibration,  is  exactly  the  same  as  the  pitch  or  tone 
of  the  exciting  waves  or  vibrations. 

Synchronism.— The  simultaneous  occurrence  of  any  wo 
events. 

A  rotating  cylinder,  or  the  movement  of  one  index  or  trail- 
ing arm,  is  brought  into  synchronism  with  another  rotating 
cylinder  or  another  index  or  trailing  arm,  not  only  when  the 
two  are  moving  with  merely  the  same  speed,  but  when  in 
addition  they  are  simultaneously  moving  over  similar  portions 
of  their  respective  paths. 

In  the  Breguet  Step-by-Step  or  Dial  Telegraph  (See  Step-by- 
Step  or  Dial  Telegraph),  the  movements  of  the  needle  on  the 
Indicator,  are  synchronized  with  the  movements  of  the  needle 
on  the  Manipulator.  In  systems  of  Fac-Simile  Telegraphy,  the 
movements  of  the  transmitting  apparatus  are  synchronized 
with  that  of  the  receiving  apparatus.  In  Delany's  Synchro- 
nous Multiplex  Telegraph  System,  the  trailing-arm  that 
moves  over  a  circular  table  of  contacts  at  the  transmitting 
end,  is  accurately  synchronized  with  a  similar  trailing-arm 
moving  over  a  similar  table  at  the  receiving  end. 

Delany,  who  was  the  first  to  obtain  rigorous  synchronism 
at  the  two  ends  of  a  telegraphic  line  hundreds  of  miles  in 
length,  accomplises  this  by  the  use  of  La  Cour's  phonic  wheel, 
through  the  agency  of  correcting  electric  impulses,  automat- 
ically sent  in  either  direction  over  the  main  line,  when  one 
trailing  arm  gets  a  short  distance  in  advance  or  back  of  the 
other. 

Synchronous    Multiplex    Telegraphy.— (See    Tele- 

</r(tj>h//,  Synchronous  Multiplex.) 

System,  Astatic (See  Astatic  System.) 


574  A  DICTIONARY  OF  ELECTRICAL 

System,  Block of  Railway  Telegraphy.— 

(See  Block  System  for  Railways.) 

System,    Centimetre-Gramme-Second  of 

Measurement. — (See  Centimetre- Gramme-Second  System 
of  Measurement.) 

Systems  of  Distribution  by  Alternating  Currents. 

— System  of  electric  distribution  by  the  use  of  alternating 
currents. 
Such  a  system  embraces, 

(1)  An  Alternating-Current  Dynamo-Electric  Machine. 

(2)  A  Conductor  or  Line  Wire  having  a  metallic  circuit. 

(3)  A  number  of  Converters  whose  primary  coils  are  placed 
in  the  circuit  of  the  line  wire. 

(4)  A  number  of  Electro  Receptive  Devices  placed  in  the  cir- 
cuit of  the  secondary  coil  of  the  converter. — (See  Converter  or 
Transformer.) 

Systems  of  Distribution  by  Constant  Currents.— 

Systems  for  the  distribution  of  electricity  by  means  of  constant 
currents. 

Distribution  by  means  of  constant  currents  may  be  effected 
in  a  number  of  ways ;  the  most  important  are  • 

(1)  Distribution  with  Constant  Current  or  Series  Distribu- 
tion. 

(2)  Distribution  with  Constant  Potential  or  Multiple  Distri- 
bution. 

In  a  System  of  Series  Distribution,  the  electro  receptive  de- 
vices are  placed  in  the  main  line  in  series,  so  that  the  electric 
current  passes  successively  through  each  of  them.  In  such  a 
system  each  device  added  increases  the  total  resistance  of  the 
circuit. 

In  order  therefore  to  maintain  the  current  strength  constant, 
independent  of  the  number  of  devices  added,  the  electro- 
motive force  of  the  source  must  increase  with  each  electro- 
receptive  device  added,  and  decrease  with  each  electro-  recep- 


WORDS,  TERMS  AND  PHRASES.  575 

tive  device  taken  out.  If  the  number  of  electro-receptive  de- 
vices be  great,  such  a  circuit  is  necessarily  characterized  by  a 
comparatively  high  electro-motive  force. 

Since  the  current  passes  successively  through  all  the  electro- 
receptive  devices,  an  automatic  safety  device  is  necessary  in 
order  to  automatically  provide  a  short  circuit  of  comparatively 
low  resistance  past  the  faulty  device,  and  thus  prevent  a 
single  faulty  device  from  invalidating  the  action  of  all  other 
devices  in  the  circuit. 

Arc  lamps  are  usually  connected  to  the  line  circuit  in  series. 

In  a  System  of  Multiple  Distribution,  the  electro-receptive  de- 
vices are  connected  with  the  main  Jine  or  leads  in  multiple-arc, 
or  parallel,  so  that  each  device  added  decreases  the  resistance 
of  the  circuit.  In  order,  therefore,  to  maintain  a  proper 
current  through  the  electro-receptive  devices,  the  mains  must 
be  kept  at  a  nearly  constant  difference  of  potential.  The 
electro-receptive  devices  employed  in  such  a  system  of  dis- 
tribution are  generally  of  high  electric  resistance,  so  that  the 
introduction  or  removal  of  a  few  of  the  electro-receptive  devices 
will  not  materially  alter  the  resistance  of  the  whole  circuit, 
and  will  not,  therefore,  materially  affect  the  remaining  lights. 

In  this  system  automatic  safety  devices,  operating  by  the 
fusion  of  a  readily  melted  alloy  or  metal,  are  provided  for  the 
purpose  of  preventing  too  powerful  currents  from  passing 
through  any  branch  connected  with  the  main  conductors  or 
leads.—  (See  Plug,  Fusible.) 

Incandescent  lamps  are  generally  connected  with  the  main 
conductors  or  leads  in  parallel  or  multiple-arc. 

Distribution  of  incandescent  lamps  by  series  connections  is 
sometimes  employed.  Such  lamps  are  usually  of  compara- 
tively low  resistance,  and  are  provided  each  with  an  auto- 
matic cut-out,  whicli  establishes  a  short  circuit  past  the  lamp 
on  its  failure  to  properly  operate. 

During  tho  passage  of  an  electric  current  through  any  series 
distribution  circuit,  energy  is  expended  in  different  portions  of 


576  A  DICTION  AKY  OF  ELECTRICAL 

the  circuit,  in  the  proportion  of  the  resistance  of  these  parts. 
In  any  system,  economy  ot  distribution  necessitates  that  the 
energy  expended  in  the  electro-receptive  devices  must  bear  as 
Jarge  a  proportion  as  practicable  to  the  energy  expended  in 
the  source  and  leads.  In  series  distribution,  this  can  readily 
be  accomplished  even  if  the  resistance  of  the  ieads  is  com- 
paratively high  since  the  total  resistance  of  the  circuit  in- 
creases with  every  electro-receptive  device  added.  Compara- 
tively thin  wires  can  therefore  be  employed,  for  a  very  con- 
siderable extent  of  territory  covered,  without  considerab  :e  'oss. 

In  systems  of  multiple  distribution,  however,  this  is  impos- 
sible ;  for,  since  every  electro-receptive  device  added  de. 
creases  the  total  resistance  of  the  circuit,  unless  the  resistance 
of  the  leads  is  correspondingly  decreased  the  economy  be- 
comes smaller,  unless  the  resistance  of  the  leads  was  orig- 
inally so  low  as  to  be  inappreciable  as  compared  with  the 
change  of  resistance. 

In  systems  of  distribution  by  alternating  currents,  this  is 
avoided  by  passing  a  current  of  but  small  strength  and  con- 
siderable difference  of  potential  over  a  line  connecting  distant 
stations,  and  converting  this  current  into  a  current  of  large 
strength  and  small  difference  of  potential  where  it  is  required 
for  use. 

Tachograph.— An  apparatus  for  recording  the  number 
of  revolutions  of  a  shaft  or  machine  per  minute. 

Tachometer,  or  Speed  Indicator.— An  apparatus 
for  determining  the  number  of  revolutions  of  a  shaft  or  ma- 
chine per  minute. 

Various  forms  of  apparatus  are  employed  for  this  purpose. 

Tachyphore. — A  term  proposed  by  Wurtz  for  a  system 
of  electric  transportation,  in  which  a  carriage  of  magnetic 
material  is  propelled  by  the  sucking  action  of  solenoids 
placed  along  the  track  and  energized  in  succession  during  the 
passage  of  the  car. 


WORDS,  TERMS  AND  PHRASES. 


577 


Tangent. — One  of  the  trigonometrical  functions.  (See 
( Trigonometry.) 

Tangent  Galvanometer. — A  galvanometer  in  which 
the  current  strength  passing  through  the  deflecting  coil  is  pro- 
portional to  the  tangent  of  the  angle  of  deflection  it  produces 
in  the  needle.  (See  Galvanometer,  Tangent.) 

Tangent  Scale.— A  scale  designed  for  use  with  a  galvano- 
meter, on  which  the  values  of  the  tangents  are  marked,  in- 
stead of  equal  degrees  as  ordinarily,  thus  avoiding  the  neces- 
sity of  finding  from  tables  the  tangents  corresponding  to  the 
degrees. 

Such  a  scale  may  be  constructed  as  follows:  Draw  the 
tangent  B  T,  to  the  circle,  Fig.  362,  and  lay  off  on  it  any  num- 
ber of  equal  divisions  or  parts  as,  for  example,  the  thirty 
shown  in  the  annexed  figure.  Connect  these  parts  with  the 
centre  C,  of  the  circle.  The  arc  of  the  circle  will  thus  be 


Fig.  362. 

divided  into  parts  proportional  to  the  value  of  the  tangents  of 
the  angles.  These  parts  are  more  nearly  equal  the  nearer 
they  are  to  B,  and  grow  smaller  and  smaller  the  further  they 
are  from  B.  In  tangent  galvanometers,  it  is  therefore  very 
difficult  to  accurately  determine  the  current  strength  when 
the  deflections  of  the  needle  are  very  large. 

Tape,  Insulating A  ribbon  of  flexible  material 

impregnated  with  kerite,  okonite,  rubber,  or  suitable  insulat- 
ing material  employed  for  insulating  wires  or  electric  con- 
ductors at  joints,  or  other  exposed  places. 


578  A  DICTIONARY  OF  ELECTRICAL 

Sometimes  the  tape  is  formed  entirely  of  the  above  named 
insulating  materials. 

Tapper,  Double Key. — The  key  used  in  systems 

of  needle  telegraphy  to  send  electric  impulses  through  the  line 
in  alternately  opposite  directions  as  desired.  (See  Telegraphy, 
Single  Needle.) 

Target,  Electric A  target  in  which  the  point 

struck  by  the  ball  is  automatically  registered  by  electric  devices. 

A  variety  of  targets  have  been  devised ;  generally,  how- 
ever, the  target  is  divided  into  a  number  of  separate  sections, 
provided  with  circuits  of  wires  on  the  making  or  breaking  of 
any  of  which,  by  the  impact  of  the  ball,  the  section  struck 
is  automatically  indicated  on  an  electric  annunciator. 

Teazer,  Electric  Current A  name  employed 

by  Brush  for  a  field  magnet  shunt  circuit  around  the  external 
circuit  of  his  dynamo-electric  plating  machine.  (See  Dynamo- 
Electric  Machine,  Shunt.) 

Tel- Autograph. — A  telegraphic  system  for  the  f ac-simile 
reproduction  of  handwriting. 

Tele-Barometer,  Electric An  electric  record- 
ing barometer  for  indicating  and  recording  barometric  or 
other  pressure  at  a  distance. 

Telegraph,  Electric An  apparatus  for  the 

electric  transmission  of  signals  between  stations  connected  by 
electric  conductors. 

Various  systems  of  telegraphy  are  in  common  use,  all  of 
which,  however,  consist  of  various  forms  of  the  following 
apparatus,  viz. : 

(1)  Transmitting  Apparatus,  by  means  of  which  electrical 
impulses  are  sent  into  the  line. 

(2)  Receiving  Apparatus,  by  means  of  which  the  electric 
impulses  are  caused  to  produce  visible  or  audible  signals, 
which  may,  or  may  not,  be  permanently  recorded. 

(3)  A  Conducting  or  Line  Wire  connecting  the  two  stations. 


WORDS,  TERMS  AND  PHRASES.  579 

(4)  Main  and  Local  Batteries  for  producing  the  currents 
employed  in  the  transmission  and  reception  of  the  signals. 

(5)  Various  Relays  and  Repeaters,  employed  on  long  lines, 
in  order  to  permit  additional  local  batteries  to  be  used  to  carry 
the  electric  impulses  over  longer  lines  than  could  otherwise 
be  employed. 

Telegraphic  Code. — (See  Alphabet,  Telegraphic.) 
Telegraphic  Embosser.— (See  Embosser,  Telegraphic.) 
Telegraphic  Joints. — (See  Joints,  Telegraphic.) 
Telegraphic  Needle.— (See  Needle,  Telegraphic.) 
Telegraphic  Switch  Board.— A  device  employed  at  a 

telegraph  station  by  means  of  which  any  one  of  a  number  of 

telegraph  instruments,  in  use  at  that 

station,  may  be  placed  in,  or  removed 

from,    any    line    connected    with    the 

station. 
In  the  switch  board  shown  in  Fig. 

363,  the  upper  left  hand  binding  post 

is  connected  to  earth ;    the  four   re- 
maining binding  posts  are  connected 

to  two  separate  instruments.     The  sec- 
ond and  third  from  the  top,  to  one 

instrument,  and  the  fourth  and  fifth, 

to  another  instrument.    The  four  posts 

at  the  top  of  the  figure  are  connected  to  two  lines  running 

east  and  west. 
Various  connections  are  made  by  the  insertion  of  plug  keys 

in  the  various  openings. 

Telegraphy,  American  or  Ulorse  System  of 

— In  the  Morse  system,  as  now  generally  employed  in  America, 
the  transmitting  apparatus  consists  essentially  of  a  telegraphic 
key,  by  means  of  which  the  main  line  circuit  can  be  readily 
made  or  broken  in  accordance  with  the  dots  and  dashes  of  the 
Morse  Alphabet.  (See  Alphabet,  Morse.) 


580 


A  DICTIONARY  OF  ELECTRICAL 


A  metallic  lever  A,  Fig.  364,  is  supported  on  a  pivot  at  G, 
between  two  set  screws  D,  D,  so  as  to  have  a  slight  move- 
ment in  a  vertical  plane.  This  motion  is  limited  in  one  direc- 
tion by  a  stop  at  C,  called  the  anvil  or  front  contact,  and  in 
the  other  direction  by  a  set  screw  F,  which  constitutes  its 
back  stop.  The  front  stop  C,  is  provided  with  a  platinum 
contact  or  stud,  which  may  be  brought  into  contact  with,  or 
separated  from,  a  similar  stud  placed  directly  opposite  it. 
These  contacts  are  connected  to  the  ends  of  the  circuit,  so  that 


Fig.  36k. 

on  the  movements  of  the  key,  by  the  hand  of  the  operator 
placed  on  the  insulated  head  B,  the  line  is  closed  and  broken 
in  accordance  with  the  dots  and  dashes  of  the  Morse  alphabet. 
A  spring,  the  pressure  of  which  is  regulated  by  the  screw  F', 
is  provided  for  the  upward  movement  of  the  key.  A  switch 
H,  is  provided  for  closing  the  line  when  the  key  is  not  in  use, 
since  the  system  as  generally  used  in  the  United  States  the 
line  is  operated  on  closed  circuit. 

In  the  Morse  system  each  station  is  provided  with  a  key, 
relay,  sounder  or  register,  and  a  local  battery.  The  closed 
circuit,  connecting  one  station  with  another,  being  broken  by 
the  opening  of  the  switch  H,  on  the  working  of  the  key,  so  as 


WORDS,  TERMS  AND  PHRASES.  581 

to  open  and  close  its  contacts,  the  armature  of  the  relay  opens 
or  closes  the  circuit  of  the  local  battery  and  operates  the 
sounder  or  registering  apparatus  connected  therewith.  (See 
Sounder,  Telegraphic.  Registering  Ap2)aratus,  Telegraphic.) 

Telegraphy,  Automatic  -  —Apparatus  by 

means  of  which  a  telegraphic  message  is  automatically  trans- 
mitted by  the  motion  of  a  previously  perforated  fillet  of  paper 
containing  perforations  of  the  shape  and  order  required  to 
form  the  message  to  be  transmitted. 

The  paper  passes  between  two  terminals  of  the  main  line, 
the  circuit  of  which  is  completed  when  the  terminals  come 
into  contact  at  the  perforated  parts,  and  is  broken  when  sepa- 
rated by  the  paper. 

The  advantages  of  the  automatic  telegraph  arise  from  the 
fact  that  since  the  paper  fillets  can  be  prepared  beforehand, 
great  speed  is  attained  by  their  aid.  In  the  automatic  tele- 
graph some  form  of  registering  apparatus  is  employed. 

Type-printing  telegraphs  are  often  used  for  registering 
apparatus,  in  which  case  the  impulses  required  for  the  trans- 
mission of  the  different  letters  are  automatically  sent  into  the 
line  by  the  depression  of  corresponding  keys  on  a  suitably 
arranged  key -board. 

Telegraphy,  Chemical (See  Recorder, 

Bain's  Chemical.) 

Telegraphy,  Dial (See  Telegraph,  Step-by - 

Step.) 

Telegraphy,  Double  Needle A  system  of 

needle  telegraphy  in  which  two  separate  and  independently 
operated  needles  are  employed. 

This  system  differs  from  the  single  needle  system  only  in 
the  fact  that  two  needles,  entirely  independent  of  each  other 
are  mounted  side  by  side,  on  the  same  dial,  so  as  to  permit 
their  simultaneous  operation  by  the  right  and  left  hand  of  the 
operator.  Each  needle  has  therefore  a  separate  wire.  The 


582 


A  DICTIONARY  OP  ELECTRICAL 


increase  in  speed  of  signaling  thus  obtained  is  not,  however, 
sufficiently  great  to  balance  the  increased  expense  of  con- 
struction. Single  needle  instruments,  therefore,  are  preferred 
to  those  with  two  needles. 

Telegraphy,  Diplex  --  A  method  of  simul- 
taneously sending  two  messages  in  the  same  direction  over  a 
single  wire. 

Telegraphy,  Duplex  ---  Devices  whereby  two 
telegraphic  messages  can  be  simultaneously  transmitted  over 
a  single  wire  in-opposite  directions. 

Various  duplex  telegraphs  have  been  devised. 

The  Bridge  Duplex  is  shown  in  Fig.  365.  The  receiving  re- 
lay is  placed  in  the  cross  wire  of  a  Wheatstone's  balance. 
(See  Balance,  Wheastone's  Electric.) 


fig.  365. 

When  the  ends  of  this  cross  wire  are  at  the  same  potential, 
which  will  occur  when  the  resistances  in  the  four  arms  are 
proportionally  equal,  no  current  passes. 

The  battery  is  connected  through  the  transmitter  K,  which 
is  arranged  so  that  the  battery  contact  is  made  before  the 
connection  of  the  line  to  earth  is  broken,  to  H,  where  the 
circuits  branch  to  form  the  arms  of  the  bridge.  Adjustable  re- 
sistances A,  B,  are  placed  in  the  two  arms  of  the  bridge.  The 
line  wire  L,  connected  as  shown,  forms  the  third  arm  and  a 


WORDS,  TERMS  AND  PHRASES. 


583 


rheostat  or  other  adjustable  resistance  R,  connected  to  a  con- 
denser C,  as  shown,  forms  the  fourth  arm.  (See  Rheostat.)  The 
relay  M,  is  placed  in  the  cross  wire  of  the  bridge  thus  formed. 
Small  resistances  V  and  W,  are  placed  in  the  circuit  of  the 
battery  to  prevent  injurious  short-circuiting. 

A  similar  disposition  of  apparatus  is  provided  at  the  other 
end  of  the  line.  If,  now,  the  four  resistances  at  one  end  are 
suitably  adjusted,  the  relay  will  not  respond  to  the  outgoing 
current ;  but,  since  an  earth  circuit  is  employed,  it  will  re- 
spond to  the  incoming  current.  The  relay  at  either  end,  there- 
fore, will  only  respond  to  signals  from  the  other  end.  The 
operator  may  thus  signal  the  distant  station  while,  at  the 
same  time,  his  relay,  not  being  affected  by  his  sending,  is  in 
readiness  to  receive  signals  from  the  other  end. 


Fig.  366. 

Telegraphy,  Fac-Simile,  or  Autographic or 

Pantelegraphy. — Apparatus  whereby  a  fac-simile  or  co2>y 
of  a  chart,  diagram,  or  signature  is  telegraphically  transmitted 
from  one  station  to  another. 

Bakewell's  Fac-Simile  Telegraph,  which  was  one  of  the  first 
devised,  consists  of  two  similar  metal  cylinders  c,  c',  arranged 
at  the  two  ends  of  a  telegraph  line  L,  at  M  and  M',  as  shown 
in  Fig.  366.  These  cylinders  are  synchronously  rotated  and 


584  A  DICTIONARY  OF  ELECTRICAL 

provided  with  metallic  arms  or  tracers  r,  r',  placed  on  a 
horizontal  screw  in  the  line  circuit  and  moved  laterally,  over 
the  surface  of  the  cylinder  on  its  rotation 

At  the  transmitting  station  the  chart,  writing,  or  other 
design  is  traced  with  varnish,  or  other  non-conducting  liquid, 
on  the  surface  of  the  metallic  cylinder,  as  at  M,  and  a  sheet 
of  chemically  prepared  paper,  similar  to  that  employed  in  the 
Bain  Chemical  System  is  placed  on  the  surface  of  the  receiv- 
ing cylinder  at  M'.  (See  Recorder,  Bain's  Chemical.) 

The  two  cylinders  being  synchronously  rotated,  the  metallic 
tracer  breaks  t'he  circuit  in  which  it  is  placed  when  it  moves 
over  the  non-conducting  lines  on  the  cylinder,  and  thus  causes 
corresponding  breaks  in  the  otherwise  continuous  blue  spiral 
line  traced  on  the  paper-covered  surface  of  M'. 

The  telegraph  keys  at  R,  R',  are  used  for  the  purposes  of 
ordinary  telegraphic  communication  before  or  after  the  record 
is  transmitted. 

Caselli's  Pan-Telegraph  is  an  improvement  on  Bakewell's 
Copying  Telegraph.  Better  methods  are  employed  for  main- 
taining the  synchronism  between  the  transmitting  and  re- 
ceiving instruments,  for  which  purpose  a  pendulum,  vibrating 
between  two  electro  magnets,  is  employed. 

Telegraphy,  Fire  Alarm A  system  of  tele- 
graphy by  means  of  which  alarms  can  be  sent  to  a  central 
station,  or  to  the  fire  engine  houses  in  the  district,  from  call 
boxes  placed  in  the  line. 

The  alarms  are  generally  sounded  by  an  apparatus  similar 
to  a  district  call,  so  that  the  pulling  back  of  a  lever  rotates  a 
wheel,  by  means  of  which  a  series  of  makes  and  breaks  are 
produced,  the  number  and  sequence  of  which,  enable  the 
receiving  stations  to  locate  the  particular  box  from  which  the 
signal  is  sent. 

In  the  case  of  some  buildings,  the  alarms  are  automatic, 
and  either  call  for  help  from  the  central  office,  or  for  the 
watchman  in  the  building,  or  else  turn  on  a  series  of  water 


WORDS,  TERMS  AND  PHRASES.  585 

faucets  or  jets,  in  order  to  extinguish  the  fire.     In  these  cases 
thermostats  are  used.     (See  Thermostats.) 
Telegraphy,    Cray's    Harmonic    multiple  — 

A  system  for  the  simultaneous 

transmission  of  a  number  of  separate  and  distinct  musical 
notes,  over  a  single  wire,  which  separate  tones  are  utilized 
for  the  simultaneous  transmission  of  an  equal  number  of  tele- 
graphic messages. 

The.  separate  tones  are  thrown  into  the  lines  by  means 
of  tuning  forks  automatically  vibrated  by  electro-magnets. 
These  forks  interrupt  the  circuit  of  batteries  connected  with 
the  main  line  at  the  transmitting  end  of  the  line.  The  com- 
posite tone  thus  formed,  is  separated  into  its  component  tones  by 
receiving  electro-magnets  called  Harmonic  Receivers,  the  arm- 
ature of  each  of  which  consist  of  a  steel  ribbon  or  plate  tuned 
to  one  of  the  separate  notes  sent  into  the  line.  As  the  com- 
plex or  undulatory  current  passes  through  the  coils  of  each 
harmonic  receiver,  that  note  only  affects  the  particular  arma- 
ture that  vibrates  in  unison  with  its  ribbon  or  reed.  The  op- 
erator, therefore,  at  this  receiver  is  in  communication  only 
with  the  operator  at  the  key  of  the  circuit  that  is  sending  this 
particular  note  into  the  line.  The  same  is  true  of  the  other 
receivers. 

The  Morse  alphabet  is  used  in  this  system,  the  dots  and 
dashes  being  received  as  musical  tones.  In  practice  it  was 
found  that  there  was  no  difficulty  in  each  operator  recognizing 
the  particular  sound  of  his  own  instrument  in  receiving, 
although  many  instruments  were  in  the  same  room. 

Telegraphy,  Induction  —  A  system  for 

telegraphing  by  induction  between  moving  trains  and  fixed 
stations  on  a  railroad,  by  means  of  impulses  transmitted  by 
induction  between  the  car  and  a  wire  parallel  with  the 
track. 

In  such  a  system,  conducting  wires  directly  connecting  the 
stations  and  the  moving  trains  are  thus  dispensed  with,  and 


586  A  DICTIONARY  OF  ELECTRICAL 

the  signals  are  received  by  means  of  induction  effects  pro- 
duced between  the  moving  train  and  the  fixed  station. 

Two  systems  of  inductive  telegraphy  are  in  actual  use,  viz. : 

(1)  The  Static  Induction   System  of  W.   W.   Smith   and 
Edison,  and 

(2)  The   Current  or  Dynamic  Induction  System  of   Wil- 
loughby  Smith  and  Lucius  J.  Phelps. 

In  the  System  of  Static  Induction,  one  of  the  condensing 
surfaces  which  receives  or  produces  the  charge,  consists  oi  a 
wire  placed  on  the  road  so  as  to  come  as  near  the  top  of  the 
cars  of  the  moving  train  as  possible.  The  other  condensing 
surface  is  composed  of  the  metal  roofs  of  the  moving  cars. 
Each  condensing  surface  is  connected  to  suitable  instruments 
and  batteries,  and  to  the  earth ;  the  line  wire  at  the  fixed 
station  being  connected  to  eai'th  through  a  ground  plate,  and 
the  metal  roof  of  the  cars  to  earth  through  the  wheels  and  track. 

Under  these  circumstances  variations  in  the  charge  of 
either  of  the  condensing  surfaces  produce  inductive  impulses 
that  are  received  by  the  other  surface  as  telegraphic  signals. 

The  Morse  alphabet  is  employed,  but  in  place  of  the  or- 
dinary receiver  or  sounder,  a  telephone  is  used. 

In  the  System  of  Current  Induction,  the  line  wire  is  placed 
near  the  track,  so  as  to  be  parallel  with  a  coil  of  insulated 
wire  placed  on  the  side  of  the  car  and  which  receives  the  in- 
ductive impulses.  The  coil  of  wire  on  the  train  is  connected 
with  instruments  and  batteries,  and  forms  a  metallic  circuit. 
The  line  wire  is  also  connected  with  suitable  batteries  and 
receiving  and  transmitting  instruments. 

An  induction  coil  is  generally  employed  since  the  greater 
and  more  rapidly  varying  difference  of  potential  of  its  second- 
ary wire  renders  it  better  suited  for  producing  effects  of  induc- 
tion. A  telephone  is  employed  as  a  receiver,  as  in  the  system 
of  static  induction.  The  metallic  car  roof  and  the  lower 
truss  rods  have  been  successfully  used  as  the  primary  and 
secondary  conductors  of  the  induction  coil. 


WORDS,  TERMS  AND  PHRASES. 


587 


The  automatic  make  and  break  used  for  operating  the  in- 
duction coil,  causes  the  Morse  characters  employed  in  this 
system  to  be  received  in  the  receiving  telephone  as  shrill  buz- 
zing sounds. 

The  receiving  telephones  used  on  'ie  trains  have  a  resist- 
ance of  about  1,000  ohms. 


Telegraphy,  multiplex 


— A  system  of  tele- 


graphy for  the  simultaneous  transmission  of  more  than  four 
separate  messages  over  a  single  wire.  (See  Telegraph,  Syn- 
chronous, Multiplex.) 

Telegraphy,  Printing A  system  of  tel- 
egraphy in  which  the  messages  received  are  printed  on  a 
paper  fillet. 

In  Callahan's  Printing   Telegraph,   two  type   wheels  are 


A  DICTIONARY  OP  ELECTRICAL 


employed,  one  of  which  carries  letter  type  and  the  other 
numerals  on  its  circumference.  These  printing  wheels  are 
placed  alongside  of  each  other,  as  shown  in  Fig.  367,  but  on 
separate  and  independent  axes. 

The  type  wheels  are  moved  by  a  step-by-step  device.  When 
the  proper  letter  or  numeral  is  reached  at  the  receiving  end, 
the  printing  wheel  is  stopped,  and  a  paper  fillet  is  pressed 
against  its  surface.  The  printing  wheel  is  kept  covered  with 
ink  by  means  of  an  inked  roller. 


Fig.  368. 

The  transmitting  instrument  is  similar  in  its  operation  to 
the  Breguet  Manipulator.  Separate  transmitters  are  used 
for  each  of  the  wires.  (See  Telegraphy,  Step-by-Step.) 

Telegraphy,  Quadruples ——A.  system  for 

the  simultaneous  telegraphic  transmission  of  four  messages 
over  a  single  wire. 


WORDS,  TERMS  AND  PHRASES. 


589 


There  are  various  systems  of  quadruplex  telegraphy.  For 
the  details  of  their  operation  the  student  is  referred  to  stand- 
ard books  on  telegraphy. 

Telegraphy,  Single  Needle A  system  of 

telegraphy  by  means  of  which  the  signals  transmitted  are  re- 
ceived by  observing  the  movements  of  a  vertical  needle  over 
a  dial. 

Movements  of  the  top  of  the  needle  to  the  right  of  the 
observer  represent  the  dashes,  and  movements  to  the  left,  the 
dots  of  the  Morse  alphabet. 


Fig.  870.  Fig.  S71. 

The  single  needle  apparatus  of  Wheatstone  and  Cooke's 
system  is  shown  in  Figs.  368  and  369.  Fig.  368,  shows  the 
external  appearance,  and  Fig.  369,  the  internal  arrangements 
as  seen  from  the  back.  An  astatic  needle  is  placed  inside  two 
coils  of  insulated  wire  C  C.  Only  one  of  these  needles  N,  is 
visible  on  the  face  of  the  receiving  instrument.  The  current 
from  the  line  enters  at  L,  passes  through  the  coil  C  C,  and 
leaves  at  N. 


590  A  DICTIOIf ARJT  OF  ELECTRICAL 

The  movements  of  the  needle  to  the  right  or  the  left  are  ob- 
tained by  changing  the  direction  of  the  current  in  the  coils 
C  C.  This  is  effected  by  working  the  handle  when  send- 
ing, and  thus  moving  the  commutator  at  S,  S,  and  bringing 
the  contact  springs  resting  thereon  into  different  contacts. 

In  the  more  modern  form  of  Single  Needle  Instrument, 
shown  in  Fig.  370,  a  single  magnetic  needle  N  S,  Fig.  371, 
only  is  placed  in  the  coil. 

This  needle  is  rigidly  attached  to  a  light  needle  a,  b,  used 
only  as  a  pointer,  and  is  alone  visible  in  the  front  of  the  figure 
on  the  left.     The  relative  disposition  of  these 
needles  is  shown  in  the  drawing  on  the  right. 

The  reversals  of  the  current,  required  to 
deflect  the  needle  to  the  right  or  left,  are  ob- 
tained by  means  of  a  double  key  or  tapper, 
shown  in  Fig.  372. 

The  levers  L  and  E,  are  connected  respect- 
ively to  line  and  earth,  and,  when  not  in  use, 
rest  against  C,   connected  with  the  positive 
side  of  the  battery  ;  but  when  depressed  con- 
nect with  Z,  attached  to  the  negative  side  of 
Fia  372          ^e  battery.     The  depression  of  L,  therefore, 
sends  a  negative  current  into  the  line  and 
deflects  the  needle,  say,  to  the  left,  while  the  depression  of 
E  sends  a  positive    current  into  the  line  and  deflects  the 
needle  to  the  right.    The  terms  positive  and  negative  currents 
are  used  in  telegraphy  to  indicate  currents  whose  direction  is 
positive  or  negative. 

Telegraphy,  Speaking; A  system  for  the 

telegraphic  transmission  of  articulate  speech.  (See  Tele- 
phones.) 

Telegraphy,  Step-hy-Step A   system   of 

telegraphy  in  which  the  needle  of  a  dial,  or  the  type  wheel 
of  a  printing  telegraph,  is  moved  step-by-step  by  electric 
impulses  sent  over  the  line.  (See  Telegraphy,  Needle  or  Dial} 


WORDS,  TERMS  AND  PHRASES.  591 

Telegraphy,  Sub-marine —A  system  of 

telegraphy  in  which  the  line  wire  consists  of  a  sub-marine 
cable. 

In  long  sub-marine  cables,  in  order  to  avoid  retardation 
from  the  self-induction  of  the  current,  and  the  static  charge 
arising  from  the  cable  acting  as  a  condenser,  very  small 
currents  are  used.  To  detect  these  a  very  sensitive  i-eceiv- 
ing  insti*ument,  such  as  the  mirror  galvanometer,  or  the 
siphon  recorder,  is  employed.  (See  Galvanometer,  Mirror. 
Recorder,  Siphon.) 

According  to  Culley,  the  retardation  in  the  case  of  one  of 
the  sub-marine  cables  between  Newfoundland  and  Ireland, 
amounts  to  two-tenths  of  a  second  before  a  signal  sent  from 
one  end  produces  any  appreciable  effect  at  the  other  end, 
while  three  seconds  are  required  for  the  current  through  the 
cable  to  gain  its  full  strength. 

Telegraphy,  Synchronous-Multiplex,  

Delany's  System.— A  system  devised  by  Delany  for  the 
simultaneous  telegraphic  transmission  of  a  number  of 
messages  either  all  in  the  same  direction,  or  purt  in  one 
direction  and  the  remainder  in  the  opposite  direction. 

The  Delany  System  embraces  the  following  parts  : 

(1)  A  circular  table  of  alternately  insulated  and  grounded 
contacts  at  either  end  of  a  telegraphic  line. 

(2)  A  synchronized  rotating  arm  or  trailing  contact,  at  each 
end  of  the  line,  driven  by  a  phonic  wheel,  and  maintained  in 
synchronous  rotation  by  means  of  electric  impulses  automatic- 
ally sent  out  over  the  main  line  in  either  direction,  on  the 
failure  of  the  wheel  at  either  end  to  rotate  synchronously  with 
that  at  the  other  end. 

(3)  Transmitting    and    receiving    instruments    connecting 
similar  contacts  at  each  end  of  the  main  line,  and  forming  prac- 
tically separate  and  independent  lines  for  the  simultaneous 
transmission  of  dispatches  over  the  main  line  in  either  direc- 
tion. 


592  A  DICTIONARY  OF  ELECTRICAL 

The  main  line  is  simultaneously  connected  at  both  of  its  ends 
to  corresponding  operating  instruments,  and  transferred  from 
one  set  of  instruments  to  another  so  rapidly  that  the  operators, 
either  sending  or  receiving,  cannot  realize  that  the  line  has 
been  disconnected  from  their  instruments  and  given  to  others, 
because  each  of  them  will  always  have  the  line  ready  for  use, 
even  at  the  highest  rate  of  manipulation,  and  will,  therefore, 
to  all  practical  intents  and  purposes,  have  at  his  disposal  a 
private  wire  between  himself  and  the  operator  with  whom 
he  is  in  communication. 

Therefore,  although  more  than  one  operator  may  be  spoken 
of  as  simultaneously  using  the  line  at  any  given  time,  yet 
in  point  of  fact  no  two  operators  are  in  reality  absolutely 
using  it  at  the  same  time ;  but  they  follow  one  another  at 
such  short  intervals,  and  the  line  is  taken  from  one  operator 
and  transferred  to  another  so  rapidly  that  none  of  them  can 
at  any  time  tell  but  that  he  has  the  line  alone,  and  that  there- 
fore it  is  practically  open  for  the  use  of  every  operator  just  as 
if  he  alone  had  control  of  it. 

There  will,  therefore,  be  established,  by  the  use  of  a  single 
line,  as  many  private  and  separate  lines  as  there  are  trans- 
ferences of  the  line  from  the  time  it  is  taken  from  the  first 
operator,  and  again  given  back  to  him. 

This  system  has  been  extended  to  as  many  as  seventy-two 
distinct  and  separate  printing  circuits,  maintained  and  operated 
on  a  single  connecting  line  wire. 

Fig.  373,  shows  the  apparatus  at  each  end  of  the  line,  at  the 
stations  X  and  Y.  The  apparatus  at  each  end  is  substantially 
identical.  A  steel  fork  a,  at  each  station,  is  automatically 
and  continuously  vibrated  by  the  action  of  the  local  battery 
L  B,  and  the  electro-magnet  A,  called  the  vibrator  magnet. 

Platinum  contacts  x,  a?1,  placed  on  the  inner  faces  of  the 
tines  of  the  fork,  make  and  break  contact  with  delicate  con- 
tact springs  y,  y1. 

The  fork  being  mechanically  started  into  a  vibratory  mo- 


WORDS,  TEEMS  AND  PHRASES. 


593 


tion,  will  automatically  make  and  break  its  local  circuit,  and 
thus  send  impulses  into  the  fork-magnet  A,  that  will  continu- 
ously maintain  the  vibrations  of  the  fork,  m  a  well-known 
manner. 

The  making  and  breaking  of  the  contacts  x  and  y,  conse- 
quent on  the  fork's  vibration,  opens  and  closes  a  circuit  of  an- 
other local  battery  called  the  motor  circuit,  in  which  is  placed 
an  electro-magnet  D.  the  function  of  which  is  to  maintain  the 
continuous  rotation  of  the  transmission  apparatus  C. 


Fig.  sis. 

The  continuous  vibration  of  the  fork  makes  and  breaks  the 
contacts  at  x  and  y,  and  thereby  makes  and  breaks  the  motor 
<'ircuit.  The  alternate  magnetizations  and  demagnetizations 
of  the  cores  of  the  motor-magnet  D  cause  the  rotation  of  the 
transmission  apparatus  C. 

The  motor-magnet  and  transmission  wheel  or  disc  C,  pro- 
vided with  projections  c,  c,  is  the  invention  of  Paul  La  Cour, 
and  is  styled  by  him  a  '  Phonic  Wheel," 


594 


A  DICTIONARY  OF  ELECTRICAL 


The  transmission  apparatus  is  illustrated  in  detail  in  Figs. 
374  and  375,  and  is  an  exact  counterpart  of  the  receiving  appar- 
tus  at  the  other  end  of  the  line.  A  base  plate  E,  provided  with 


Mg. 


binding  posts,  carries  a  vertical  rotary  shaft  F.  A  circular 
table  F1,  is  provided  with  a  series  of  insulated  contacts  ar- 
ranged symmetrically  around  the  axis  of  rotation  of  the  shaft. 


Fig.  375. 

A  radial  arm  F2,  connected  with  the  shaft  F,  carries  at  its 
outer  extremity  a  trailing  contact  finger  /.  As  the  disc  C  is 
rotated  by  the  electro-magnet  D,  the  trailing  contact  f, 


WORDS,  TERMS  AND  PHRASES.  595 

sweeps  around  the  circular  table  F1,  and  is  brought  success- 
ively into  contact  with  the  insulated  contact-pieces  placed  on 
the  upper  face  of  the  table  F1. 

The  main  line  Q.  Q,  has  one  of  its  ends  connected  with  the 
trailing-  finger  /.  As  the  shaft  F,  rotates,  the  line  is  therefore 
brought  into  successive  electrical  connection  with  the  series 
of  insulated  contacts  in  the  upper  face  of  the  table  F1. 

Any  suitable  number  of  insulated  contacts  may  be  placed 
on  the  circular  table  F1  ;  sixty  are  shown  in  Fig.  376  In 
practice  these  contacts  are  connected  in  accordance  with  the 
number  of  circuits  which  it  is  desired  to  simultaneously 
maintain  on  the  same  wire.  In  the  special  case  shown 
in  the  figure  referred  to  above,  it  is  arranged  so  that 
four  separate  circuits  shall  be  established  on  the  same  line 
wire.  The  sixty  contacts  are  placed  in  six  independent  series, 
numbered  from  1  to  10,  consecutively.  In  the  arrangement 
here  shown  two  of  the  contact  pieces  in  each  series  of  ten 
are  connected  tn  the  same  circuit,  and  as  there  are  six  series, 
each  of  the  circuits  so  connected  will  have  twelve  contacts 
for  each  rotation  of  the  disc,  and  twelve  electrical  impulses, 
as  will  be  afterwards  described 

The  detailed  mechanism  by  means  of  which  the  separate 
and  independent  circuits  so  obtained  are  utilized  for  the  trans- 
mission and  reception  of  messages  is  shown  in  Fig.  376  R, 
R1,  R2  and  R8  are  polarized  relays;  S,  S1,  S8  and  S8  are  ordi- 
nary Morse  sounders,  although  in  the  practice  of  this  inven- 
tion some  improvement  has  been  introduced  in  connection 
with  the  receiving  instruments.  The  connections  with  the 
main  and  the  local  batteries  M  B  and  L  B,  are  clearly  shown 
in  the  figure. 

It  will  be  noticed  that  the  relay  R  is  connected  with  the  wire 
r,  and  with  the  contacts  1  and  5 ;  R1,  is  connected  by  r1,  with 
the  contacts  2  and  6  ;  R2,  by  the  wire  r2,  with  the  contacts  3 
and  7;  and  R8,  by  the  wire  r8,  with  the  contacts  4  and  8  Sim- 
ilar instruments  and  circuits  are  placed  at  each  end  of  the  line. 


596 


A  DICTIONARY  OF   ELECTRICAL, 


Without  further  describing  the  operation  of  the  instruments 
shown  in  the  figure,  it  need  -only  now  be  borne  in  mind  that 
the  corresponding  relays  at  the  distant  stations  are  connected 
with  the  correspondingly  numbered  contacts  When,  there 
fore,  the  trailing  contact  finger  at  each  station  simultaneously 
touches  the  contacts  bearing  the  same  number,  the  corre- 


Fife 

=rV i_  II,  i 


Fig.  376 

spending  instruments  connected  with  these  contacts  at  each 
station  will  be  placed  in  communication  over  the  mam  line, 
the  trailing  contact  finger/,  completing  the  connection  of  the 
mam  line  with  the  contact  arm  in  the  manner  already  de- 
scribed. 


Telegraph) ,  Time 

graphic  transmission  of  time. 


—A  system  for  the  tele- 


WORDS,  TERMS  AND  PHRASES. 


597 


A  system  of  time-telegraphy  includes  a  master  clock,  the 
movements  of  whose  pendulum  automatically  transmit  a 
number  of  electric  impulses  to  a  number  of  secondary  clocks 
and  thus  moves  them  ;  or  self  winding  clocks  are  employed, 
which  are  corrected  daily  by  an  impulse  sent  over  the  line 
from  a  master  clock. — (See  Clocks,  Electric.} 


Tele-Manometer,  Electric 


•  — A  gauge  for  elec 


trically  indicating  and  recording  pressure  at  a  distance. 


Fig.  SSL 

The  tele-manometer  includes  a  pressure  gauge  furnished  with 
electric  contacts  operated  by  the  movements  of  the  needle  of 
the  steam  gauge  for  instance,  and  indicating  and  recording 
apparatus.  An  alarm  bell  is  provided  to  call  attention  to  any 
rise  of  the  pressure  above,  or  its  fall  below  the  given  or  pre- 
determined limits  for  which  the  hands  have  been  set. 


598  A  DICTIONARY  OF  ELECTRICAL 

Telemeter. — An  apparatus  for  electrically  indicating-  and 
recording  at  a  distance,  the  pressure  on  a  gauge,  the  reading 
of  a  thermometer,  or  the  indications  of  similar  instruments. 
(See  Tele-Barometer.  Tele-Manometer.  Tele-Thermometer.) 

Teleplierage. — A  system  (Fleeming  Jenkin)  for  the  con- 
veyance of  carriages  suspended  from  electric  conductors,  and 
driven  by  means  of  electric  motors,  that  take  directly  from 
the  conductors  the  current  required  to  energize  them. 

Two  lines  are  provided,  an  up  and  a  down  line,  that  cross 
each  other  at  regular  intervals.  Each  line  is  in  segments,  and 
the  alternate  segments  are  insulated  from  each  other,  but  are 
connected  electrically  by  cross  pieces  on  the  supporting  posts. 
In  this  way  the  line  shown  in  Fig.  382,  is  obtained. 


Fig.  382. 

The  two  lines  are  maintained  at  a  difference  of  potential 
by  a  dynamo-electric  machine  at  D,  Fig.  382.  As  the  train  at 
L  T,  or  L'  T',  is  of  such  a  length  as  to  come  into  contact  with 
two  different  segments  at  the  same  time,  it  receives  a  current 
sufficient  to  run  the  motor  connected  with  it,  the  current  being 
received  through  a  conductor  joining  a  pair  of  wheels  that 
are  insulated  from  the  truck. 

The  general  arrangement  of  the  line  is  shown  in  the  an- 
nexed Fig.  381. 

Telephone. — An  apparatus  for  the  electric  transmission 
of  articulate  speech. 

The  articulating  telephone,  though  first  brought  into  public 
use  by  Bell,  was  invented  by  Reis,  in  Germany,  in  1861.  In 
America,  after  very  protracted  litigation,  Bell  has  been  decided 


•WORDS,  TERMS  AND  PHRASES. 


599 


legally  to  be  the  first  inventor,  but  scientific  men  very  gener- 
ally recognize  the  principles  of  the  invention  to  be  fully  an- 
ticipated by  the  earlier  instruments  of  Reis.  Bell,  however, 
is  justly  entitled  to  credit  for  his  improvements  in  the  Reis 
apparatus. 

In  Bell's  Magneto-Electric  Telephone,  the  transmitting  and 
receiving  instruments  are  identical.  A  coil  C,  of  insulated 
wire  connected  with  the  line,  is  placed  on  a  core  of  magnetized 
steel,  mounted  opposite  the  centre  of  a 
circular  diaphragm  of  thin  sheet  iron, 
rigidly  supported  at  its  edges. 

In  transmitting,  the  message  is  spoken 
into  the  mouth-piece  at  one  end,  as  at  D, 
in  Fig.  378,  and  the  to-and-f  ro  motions  thus 
imparted  to  the  metallic  diaphragm  at- 
tached to  the  mouth-piece  P,  produce  in- 
duction currents  in  the  coil  C,  on  the 
magnet  M.  (See  Induction,  Electro  Mag- 
netic.) These  impulses,  passing  over  the 
main  line  E  L,  produce  similar  movements 
in  the  diaphragm  P',  of  the  receiving  in- 
strument, at  D',  and  thus  causes  it  to  repro- 
duce the  message,  in  articulate  sounds,  to  one  listening  at  the 
receiving  instrument.  A  ground  circuit  is  shown  in  the  figure, 
as  usually  employed  in  practice. 

A  magneto  -  telephone 
constitutes  in  reality  a 
magneto -electric  ma- 
chine, driven  or  propelled 
by  the  voice  of  the  speak- 
er, in  which  the  currents 


Fig.  378. 


so  produced  instead  of  being  commuted  are  employed  uncom- 
muted  to  reproduce  the  uttered  speech. 

In  actual  practice  this  instrument  is  replaced  by  the  electro- 
magnetic telephone,  in  which  the  to-and-fro  motions  of  Ihc 


600  A  DICTIONARY  OF  ELECTRICAL 

transmitting  diaphragm  are  caused  to  vary  the  resistance  of  a 
button  of  carbon,  or  a  variable  contact-transmitter  similar 
to  that  employed  by  Reis  in  some  of  his  instruments.  The 
variable  resistance  is  placed  in  the  circuit  of  a  battery,  so 
that  on  speaking  into  the  transmitter,  electric  impulses  are 
sent  over  the  line  and  are  received  by  a  telephone  with  a 
magnet  core  provided  with  a  coil  in  the  main  line  circuit. 

The  telephone  is  arranged  for  actual  commercial  use  in  the 
United  States  in  the  manner  shown  in  Fig.  379. 
Telephone,  Electro-Capillary  —     —A  telephone  in 
which  the  movements  of  the  transmitting 
diaphragm  produce  currents  by  means  of 
variations  in  the  electro-motive  forces  of 
the  contact  surfaces  of  liquids  in  capillary 
tubes.     (See    Electro    Capillary    Phe- 
nomena.) 

In  Breguet's  telephone  both  the  trans- 
mitting and  the  receiving  instruments  are 
similar  in  construction  and  operate  by 
means  of  electro-capillary  phenomena. 
A  vertical  capillary  tube  communicates 
at  its  upper  end  with  an  air  space  below 
a  diaphragm,  and  at  its  lower  end  with  a 
mercury  surface  on  which  rests  a  layer  of 
acidulated  water.  A  line  wire  connects 
the  mercury  reservoirs  of  the  transmit- 
ting and  receiving  instruments,  the  remainder  of  the  circuit 
being  formed  by  another  wire  connecting  the.  mercury  near 
the  upper  parts  of  the  two  vertical  tubes. 

The  alterations  in  the  contact  surfaces  at  the  transmitting 
end  produced  by  the  movements  of  the  diaphragm,  cause 
electric  impulses  that  produce  similar  movements  of  the  dia- 
phragm at  the  receiving  end. 

Telephone,  Electro-IHotographic  —  —  or  Edi- 
son^ Electro-Chemical  Telephone.— A  telephone  in 


WORDS,  TERMS  AND  PHRASES.  601 

which  the  receiver  consists  of  a  diaphragm  of  mica  or  other 
elastic  material  operated  on  the  principle  of  the  electro-moto- 
graph. 

A  straight  lever,  which  forms  part  of  the  line  circuit  is 
rigidly  attached  at  one  end  to  the  centre  of  the  receiving 
diaphragm  and  rests  near  its  other  end  on  the  moistened  sur- 
face of  a  chalk  cylinder,  maintained  in  rotation  by  suitable 
mechanical  means.  Electric  impulses  being  sent  into  the  line 
by  the  voice  of  a  speaker  talking  at  a  transmitter  of  ordinary 
construction,  produce  slipping  movements  of  the  cylinder 
that  reproduce  in  the  receiving  diaphragm  articulate  speech. 

Telephonic  Exchange. — (See  Exchange,  Telephonic.) 

Telephonic  Joint§  of  Wire.— (See  Joints,  Tele- 
graphic.) 

Telephote  or  Pherope.— An  apparatus  for  the  tele- 
graphic transmission  of  pictures  through  the  action  of  light 
on  selenium.  (See  Telephotography.) 

Telephotography. — A  system  for  fac-simile  transmis- 
sion by  means  of  dots  and  lines  transmitted  by  means  of  a 
continuous  current  whose  intensity  is  varied  by  a  transmitting 
instrument,  containing  a  selenium  resistance.  (See  Tele- 
graph, Fac-Simile.  Selenium  Resistance.) 

The  transmitter  consists  of  a  dark  box,  mounted  on  an  axis, 
so  as  to  be  capable  of  a  sidewise  motion.  The  picture  to  be 
transmitted  is  thrown  continuously  on  the  face  of  the  box  by 
any  lantern  projection  apparatus,  and  a  small  opening  con- 
taining a  selenium  resistance  receives  the  alternations  of 
light  and  shade,  and  transmits  the  same  as  variations  in  the 
strength  of  the  otherwise  continuous  current  in  the  circuit  of 
which  the  selenium  resistance  is  placed.  The  picture  is  re- 
ceived at  the  other  end  on  a  sheet  of  chemically  prepared 
paper  moved  synchronously  with  the  transmitting  box. 

Telescope,  Reading— A  telescope  employed 

in  electric  measurements,  for  reading  the  deflections  of  the 
galvanometer. 


602 


A  DICTIONARY  OF  ELECTRICAL 


A  mirror,  suspended  above  the  needle  on  the  same  fibre  that 
holds  the  needle,  reflects  a  spot  of  light  on  a  scale  by  which 
the  amount  of  deflection  is  indicated.  (See  Galvanometer, 
Mirror.) 

A  form  of  reading  telescope  is  shown  in  Fig.  380.  An 
illumined  scale  M,  receives  the  spot  of  light  reflected  from  the 
mirror  attached  to  the  galvanometer  suspension,  and  the 
deflection  is  observed  in  the  mirror  by  the  telescope  F. 

Teleseme.— A  self-registering  hotel  annunciator,  by  means 
of  which  a  dial  operated  in  a  room,  indicates  on  the  an- 
nunciator the  article    or    service 
required. 

Tele-Thermometer,  Elec- 
tric   An  electric  record- 
ing thermometer  for  indicating 
and  recording  temperature  at  a 
distance. 

Temperature  Alarm.— (See 
Alarm,  Fire,  etc.) 
Temperature,    Effects    of 

on  Electric  Resistance. 

—(See  Resistance,  Effects  of  Tem- 
perature on.) 

Tension,  Electric 

Fig.  380.  A  term  often  loosely  applied  to 

signify  electro-motive  force,   dielectric   stress,   difference  of 
potential. 

This  term  is  now  very  generally  abandoned. 
Terrestrial  magnetism. — (See  Magnetism  Terrestrial.) 
Testing,  methods  of (See  Measurements,  Elec- 
tric.) 

Therm.— A  heat-unit  recently  proposed  by  the  British  As- 
sociation. 
A  therm  is  the  amount  of  heat  required  to  raise  the  temper- 


WORDS,  TERMS  AND  PHRASES.  60S 

ature  of  one  gi-amme  of  pure  water  at  the  temperature  of  its 
maximum  density  one  degree  centigrade.     (See  Calorie.) 

Thermo-EIectric  Battery. — (See  Battery,  Thermo- 
EIectric.) 

Thermo-EIectric  Couple.— Two  dissimilar  metals 
joined  so  as  to  produce  thermo-electric  currents  through  dif- 
ferences of  temperature. 

Tliermo-Electric  Diagram. — (See  Diagram,  Thermo- 
EIectric.) 

TIiermo-EIectric  Inversion.— An  inversion  of  the 
thermo-electric  power  of  a  couple  at  certain  temperatures 
(See  Diagram,  Thermo-EIectric.) 

Thermo-Electricity.— Electricity  produced  by  differ- 
ences of  temperature  at  the  junctions  of  dissimilar  metals. 

If  a  bar  of  anti-  p 

mony    is    soldered 
to  a  bar  of  bismuth, 

and  their  free  ends  **$&  H  C 

connected  by 
means  of  a  galvan- 
ometer, the  appli- 
cation of  heat  to  ~  fig.  381. 
the  junction,  so  as  to  raise  its  temperature  above  the  rest  of 
the  circuit,  will  produce  a  current  across  the  junction  from  the 
bismuth  to  the  antimony,  (against  the  alphabet,  or  from  B  to 
A).  If,  the  junction  be  cooled  below  the  rest  of  the  circuit,  a 
current  is  produced  across  the  junction  from  the  antimony  to 
the  bismuth,  (with  the  alphabet,  or  from  A  to  B).  These  cur- 
rents are  called  thermo-electric  currents,  and  are  proportional 
to  the  differences  of  temperature. 

Even  the  same  metal,  in  different  physical  states  or  condi- 
tions, such  as  a  wire,  part  of  which  is  straight  and  the  remain- 
der bent  into  a  spiral  as  at  H  C,  Fig.  881,  if  heated  at  F  by 
the  flame  of  a  lamp  will  show  a  current  developed  in  it. 


604 


A  DICTIONARY   OF  ELECTRICAL 


The  same  thing  may  also  be  shown  by  placing  a  cylinder  of 
bismuth  J,  Fig.  382,  in  a  gap  in  a  hollow  rectangle  of  copper 
A  B,  inside  of  which  a  magnetic  needle  M  is  supported. 

A 


Fig.  S83. 

The  rectangle  of  copper  being  placed  in  the  magnetic  me- 
ridian, on  heating  the  junction  by  the  flame  of  a  lamp  F,  the 
needle  will  be  deflected  by  a  current  produced  by  the  differ- 
ence of  temperature. 

Tnermo-EIectric  Pile,  Differential (See 

Differential  Thermo-Electric  Pile.) 


Fig.SSU. 

Thermo-Electric  Pile  or  Battery.— A  number  of 
separate  thermo-electric  couples,  united  in  series,  so  as  to 
form  a  single  thermo-electric  source. 


WORDS,  TERMS  AND  PHRASES. 


605 


Figs.  383,  and  384,  show  Nobili's  Therrao-Pile,  in  which  a 
number  of  bismuth-antimony  thermo-electric  couples  are  con- 
nected in  a  continuous  series,  as  shown  in  Fig.  386,  and  insu- 
lated from  one  another,  except  at  their  junctions,  and  packed 
in  a  metallic  box,  and  supported  as  shown  in  Fig.  385.  The 
free  terminals  of  the  series  are  connected  to  binding  posts. 
Differences  of  temperature  between  the  two  faces  of  the 
pile,  where  the  junctions  are  exposed,  result  in  a  current 
whose  difference  of  potential  is  equal  to  the  sum  of  the  differ- 
ences of  potential  of  all  the  thermo-electric  couples. 

A  careful  inspection  of  the  drawing  will  show  that  the  junc- 
tions are  formed  successively  at  opposite  faces  of  the  pile,  so 
that  if  the  junctions  be  numbered  successively,  the  even  junc- 
tions will  come  at  one  face,  and  the  odd  junctions  at  the 
other.  This  is  necessary  in  order  to  permit  all  the  thermo- 
electric couples  to  add  their  differences  of  potential;  for,  if, 


as  in  Fig.  385,  a  thermo-electric  chain  be  formed,  no  currents 
will  result  from  equally  heating  any  two  consecutive  junc- 
tions J  J,  of  the  metals  A  and  B,  since  the  electro-motive 
forces  so  produced  oppose  each  other. 

Thermo  piles  have  been  constructed  by  Clamond  of  couples 
of  iron  and  an  alloy  of  zinc  and  antimony,  of  sufficient  power 
to  produce  a  voltaic  arc  whose  illuminating  power  equalled 
40  carcel  burners.  Many  practical  difficulties  exist  which  will 
have  to  be  surmounted  before  such  piles  can  be  employed  as 
commercial  electric  sources. 


606  A  DICTIONARY  OF  ELECTRICAL 

Thermo-EIectric  Power. — (See  Power,  Thermo-Elec- 
iric.) 

Thermo-EIectric  Series.— A  list  of  metals  so  arranged, 
according1  to  their  thermo-electric  powers,  that  each  metal  in 
the  series  is  electro-positive  to  any  metal  lower  in  the  list. 

Thermo  -  Electro  •  Motive  Force.  —  Electro  -  motiv e 
force,  or  difference  of  potential,  produced  at  thermo-electric 
junctions  by  differences  of  temperature. 

Thermometer,   Electric   or    Thermo- 

Electrometer. — A  device  for  determining  the  effects  of  an 
electric  discharge  by  the  movements  of  a  liquid  column  on 
the  expansion  of  a  confined  mass  of  air  through  which  the 
discharge  is  passed. 

Thermometer  Scale,  Centigrade (See  Cen- 
tigrade Scale.) 

Thermometer  Scale,  Fahrenheit (See  Fah- 
renheit Scale.) 

Thermophone. —  Any  instrument  by  means  of  which 
sounds  are  produced  by  the  absorption  of  radiant  energy. 
(See  Photophon 

A  telephone  has  been  constructed  in  which  the  motions  of 
the  receiving  diaphragm  are  effected  by  the  expansions  and 
contractions  of  a  thin  metallic  wire  connected  to  its  centre 
and  placed  in  the  circuit  of  the  main  line. 
Thermostat.—  An  instrument  for  automatically  indicat- 
ing the  existence  of  a  given  tem- 
perature by  the  closing  of  an 
*v         electric  circuit  through  the  ex- 
_J        pansion  of  a  solid  or  liquid. 

I  Thermostats  are  used  in  sys- 

_ *^       terns    of    automatic    fire    tele- 
graphy, and  in  systems  of  auto- 
mff- s86-  matic  temperature  regulation. 

Three- Wire  System.— A  system  of  electric  distribution, 
invented  by  Edison,  in  which  three  wires  are  employed, 


WORDS,  TERMS  AND  PHRASES.  607 

In  this  system  three  conductors  are  connected  to  a  source 
of  electric  energy,  Fig.  886,  and  the  difference  of  potential 
between  the  central  and  the  two  outer  conductors  is  always 
maintained  the  same.  The  lamps  or  other  electro-receptive 
devices  are  placed  in  multiple  arc  between  either  branch,  and 
so  distributed  that  the  current  in  each  branch  is  the  same. 
When  such  a  balance  is  established  no  current  flows  through 
the  central  or  neutral  conductor.  But  when  that  balance  is 
disturbed  the  surplus  current  in  one  branch  is  taken  up  by  the 
central  conductor.  This  system  effects  considerable  economy 
in  the  weight  of  wire  required. 

Thunder. — A  loud  noise  accompanying  a  lightning  dis- 
charge. 

Thunder  is  due  to  the  sudden  rush  of  the  surrounding  air  to 
fill  the  vacuous  space  accompanying  the  disruptive  discharge 
of  a  cloud.  This  space  is  caused  by  the  condensation  of  the 
vapor  formed  on  the  passage  of  the  discharge  through  drops 
of  rain  or  moisture  in  the  air,  as  well  as  by  the  expansion  of 
the  air  itself. 
Thunder-Storms,  Geographical  Distribution  of 

(See  Storms,  Thunder,  Geographical  Distribution  of '.) 

Tick,  Magnetic. A  faint  metallic  click  heard  on 

the  magnetization  and  demagnetization  of  a  magnetizable 
substance.  (See  Magnetic  Tick.) 

Time  Ball,  Electric A  ball,  supported  in  a 

prominent  position  on  a  tall  pole,  and  caused  to  fall  at  the 
exact  hour  of  noon,  or  at  any  other  predetermined  time,  for 
the  purpose  of  thus  giving  the  exact  time  to  an  entire  neigh- 
borhood. 

The  release  of  the  ball  is  effected  by  the  closing  of  an  elec- 
tric circuit,  either  automatically,  or  through  the  agency  of  an 
observer. 

Time  Cut-Outs,  Automatic.  —  —Automatic 

cut-outs  arranged  on  storage  batteries  to  cut  them  in  or  out  of 
the  circuit  of  the  charging  source,  at  predetermined  times, 


608  A  DICTIONARY  OF  ELECTRICAL 

Time  Telegraphy.— (See  Telegraphy,  Time.  Clocks, 
Electric.) 

Tongs,  Discharging —(See  Discharging  Rods.) 

Top,  Induction (See  Induction,  Top.) 

Torpedo,  Electric (See  Ray,  Electric.) 

Torsion  Balance. — (See  Balance,  Torsion.) 

Torsion  Galvanometer. — (See  Galvanometer,  Torsion.) 

Total  or  Dead  Earth.— (See  Earths.) 

Touch,  Single,  Separate  or  Double Methods 

of  Magnetization  by.— (See  Magnetization,  Methods  of.) 

Tourmaline.— A  mineral  consisting  of  natural  silicates 
and  borates  of  alumina,  lime,  iron,  etc.,  possessing  pyro- 
electric  properties.  (See  Pyro-Electricity.) 

Tower,  Electric. A  high  tower  provided  for 

the  support  of  a  number  of  electric  arc  lamps,  employed  in 
systems  of  general  illumination. 

Tower,  System  of  Electric  Lighting.— The  lighting 
of  extended  areas  by  means  of  arc  lights  placed  on  the  top  of 
tall  towers. 

The  tower-system  of  electric  illumination  is  only  applicable 
to  wide,  open  spaces,  since  otherwise  objectionable  shadows 
are  apt  to  be  formed. 

Train  Signaling.— (See  Telegraphy,  Inductive.) 

Transmission  of  Energy.— (See  Energy,  Transmis- 
sion of.) 

Transmitters,  Electric  — Various  electric  ap- 
paratus employed  in  transmitting  or  sending  the  electric  im- 
pulses over  a  telegraph  line. 

In  most  telegraphic  systems,  the  transmitting  apparatus 
consists  of  various  forms  of  keys  for  interrupting  or  varying 
the  current  In  the  telephone  the  transmitter  consists  of  a 
diaphragm  operated  by  the  voice  of  the  speaker.  (See  Tele- 
graph. Telephone.) 


WORDS,  TERMS  AND  PHRASES. 


609 


Transformer 

Transformer. ) 

Treatment,  Hydro-Carbon 


or    Converter.  — (See     Converter    or 


of  Carbons.— 


(See  Flashing  Carbons,  Process  for.) 

Trigonometry.— That  branch  of  mathematical  science 
which  treats  of  the  methods  of  determining  the  values  of  the 
angles  or  sides  of  a  triangle. 

There  are  in  every  triangle  three  sides  and  three  angles.  If 
any  three  of  these  parts  are  given,  except  the  three  angles, 
the  values  of  the  remaining  parts  can  be  determined  by  means 
of  trigonometry,  by  what  is  called  the  solution  of  the  triangle. 
Trigonometrical  Flint  lions.— Certain  quantities,  the 
values  of  which  are  dependent  on  the  length  of  the  arcs  sub- 
tended by  angles,  which  are  taken  for  the  measures  of  the 
arcs  instead  of  the  arcs  themselves. 

0  The  trigonometrical  functions  are 
the  sine,  the  co-sine,  the  tangent,  the 
co-tangent,  the  secant,  and  the  co- 
secant. These  are  generally  abreviat- 
ed,  thus,  viz.  :  sin,  cos,  tan,  cot,  sec, 
and  co-sec. 

The  Sine  of  an  angle,  or  arc,  is  the 
perpendicular  distance  from  one  ex- 
tremity of  the  arc  to  the  diameter  pass- 
ing through  the  other  extremity. 
Fig.  887.  Thug  m  Rg    387>  B  D>  is  the  sine  Qf 

the  angle  B  O  A,  or  of  the  arc,  B  A. 

The  Cosine  of  an  angle,  or  arc,  is  that  part  of  the  diameter 
which  lies  between  the  foot  of  the  sine  and  the  centre.  Thus 
D  O,  is  the  cosine  of  the  angle  B  O  A,  or  of  the  arc  B  A. 

The  cosine  of  an  arc  is  equal  to  the  sine  of  its  complement. 
Thus  E  O  B  or  B  E,  the  complement  of  B  A,  has  for  its  sine 
I  B,  which  is  equal  to  O  D.  (See  Complement  of  Angle.) 

If  the  arc  is  greater  than  a  right  angle,  or  90°,  such,  for 


610  A  DICTIONARY  OF  ELECTRICAL 

instance,  as  the  angle  TOG,  or  the  arc  B  E  F  G,  B  D  is  its  sine. 
This  is  also  the  sine  of  BOA,  or  of  B  A,  which  is  the  supple- 
ment of  TOG,  or  B  E  F  G.  Hence  the  sine  of  an  arc  is  equal 
to  the  sine  of  its  supplement. 

The  same  is  true  of  the  cosine. 

The  Tangent  of  an  angle,  or  arc,  is  a  straight  line  touching 
the  arc  at  one  extremity,  drawn  perpendicular  to  the  diameter 
at  one  end  of  the  arc,  and  limited  by  a  straight  line  connect- 
ing the  centre  of  the  circle  and  the  other  end  of  the  arc.  Thus 
C  A  is  the  tangent  of  the  angle  B  O  A,  or  the  arc  B  A. 

The  Co-tangent  of  an  angle,  or  arc,  is  equal  to  the  tangent  of 
its  complement,  thus  E  T,  is  the  co-tangent  of  the  angle, 
B  O  A,  or  the  arc  B  A. 

The  tangent  of  an  angle,  or  arc,  is  equal  to  the  tangent  of 
its  supplement.  Thus  A  C,  is  the  tangent  of  the  angle  BOA, 
or  the  arc  B  A.  It  is  also  equal  to  the  tangent  of  the  angle 
BOG,  or  the  arc  B  E  F  G,  the  corresponding  supplement  of 
the  angle  B  O  A,  or  of  the  arc  B  A. 

The  Secant  of  an  angle,  or  arc,  is  the  straight  line  drawn 
from  the  centre  of  the  circle  through  one  extremity  of  the  arc 
and  limited  by  the  tangent  passing  through  the  other  ex- 
tremity. Thus  O  C  is  the  secant  of  the  angle  B  O  A,  or  of  the 
arc  B  A. 

The  secant  of  an  arc  is  equal  to  the  secant  of  its  supple- 
ment. 

The  Co-secant  of  an  angle,  or  arc,  is  equal  to  the  secant  of 
its  complement. 

Thus  E  T  is  the  co-secant  of  the  angle  BOA,  or  of  the  arc 
B  A. 

It  will  be  observed  that  the  co-sine,  the  co-tangent  and  the 
co-secant  are  respectively  the  sine,  tangent,  and  secant  of  the 
complement  of  the  arc,  or  in  other  words,  the  complement-sine, 
the  complement-tangent,  and  the  complement-secant. 

Trolleys.— Rolling  contacts  that  move  over  the  overhead 
lines  provided  for  a  line  of  electric  railway  care,  and  carry  off 


WORDS,  TERMS  AND  PHRASES.  611 

the  current  required  to  drive  the  motor  car.  (See  Sled 
Plow.) 

Tubes,  Geissler (See  Geissler  Tubes.) 

Tubes  of  Force.— (See  Force,  Tubes  of.) 

Tubes  of  Induction.— See  Force,  Tubes  of.) 

Tubes,  Mercury Vacuous  glass  tubes  in 

which  a  flash  of  light  is  produced  by  the  fall  of  a  small  quan- 
tity of  mercury  placed  inside  it. 

The  light  is  caused  by  the  electricity  produced  by  the  friction 
of  the  mercury  in  falling  against  the  sides  of  a  spiral  glass 
tube  placed  inside  the  vacuous  tube. 

Tubes,  Plucker (See  Plucker Tubes.) 

Tubes,  Stratification  — (See  Stratification 

Tubes.) 

Type-Printing  Telegraph.— (See  Telegraph  Print- 
ing.) 

Typewriter,  Electric A  type- writing 

machine  in  which  the  keys  are  intended  to  make  the  contacts 
only  of  the  circuits  of  electro  magnets,  by  the  attractions 
of  the  armatures  of  which  the  movements  of  the  type  levers 
required  for  the  work  of  printing  are  effected. 

Electric  typewriters  secure  a  uniformity  of  impression  that 
is  impossible  to  obtain  with  hand  worked  machines;  they  also 
greatly  lessen  the  mechanical  labor  of  writing.— (See  Dynamo- 
graph.) 

Ultra  Gaseous  Matter.— A  term  sometimes  applied  to 
radiant  matter. — (See  Matter,  Radiant.) 

Underground  Conductors.  —  Electric  conductors 
placed  underground  by  actual  burial  or  by  passing  them 
through  underground  conduits  or  subioays. 

Underground  conductors,  though  less  unsightly  than  the 
ordinary  aerial  conductors,  require  to  be  laid  with  unusual  care 
to  render  them  equally  safe,  since,  when  contacts  do  occur,  all 


612 


A  DICTIONARY  OF  ELECTRICAL 


the  wires  in  the  same  conduit  are  apt  to  be  simultaneously 
affected,  thus  spreading  the  danger  in  many  different  direc- 
tions.    They  are,  however,  less  liable  to  danger  arising  from 
accidental  crosses  or  contacts. 
Undulatory  Currents. — (See  Currents,  Undulatory.) 

I 'iii  for  in  magnetic  Field.— A  field  traversed  by  the 
same  number  of  lines  of  magnetic  force  per  unit  of  area  of 
cross  section  of  the  field. — (See  Fields,  Magnetic.) 

Uniform  Potential.— A  potential  that  does  not  vary. 

An  electric  so'urce  is  said  to  generate  a  uniform  potential 
when  it  maintains  a  constant  difference  of  potential  at  the 
terminals. 

Unipolar  Induction. — A  term  sometimes  applied  to  the 
induction  that  occurs  when  a  conductor  is  so  moved  through 
a  magnetic  field  as  to  continuously  cut  its  lines  of  force. 

If  the  conducting  wire  ABC,  Fig.  388,  be  rotated  (in  a  direc- 
tion towards  the  ob- 
server) around  the 
pole  N  of  a  magnet, 
it  will  continuously 
cut  its  lines  of  mag- 
netic force  and  will 
therefore  produce  a  ] 
continuous  current 
in  the  direction  of 
the  arrows.  The  end 
A  is  supported  in  a 
recess  in  N,  while 
the  end  near  C  slides 
on  a  projection  on 
the  middle  of  the  magnet.  Unipolar  dynamos  operate  on  the 
continuous  cutting  of  lines  of  magnetic  force. 

Strictly  speaking  there  is  no  such  thing  as  a  unipolar  dyn- 
amo, ou  unipolar  induction,  since  a  single  magnetic  pole  can- 


WORDS,  TERMS  AND  PHRASES.  618 

not  exist  by  itself.  Continuous  cutting  of  lines  of  magnetic 
force,  however,  can  exist  and  produces,  unlike  the  ordinary 
bi-polar  induction,  a  continuous  current. 

Unit  Angle.— (See  Angular  Velocity.) 

Unit,  B.  A.  —  —The  British  Association  unit  of  resist- 
ance or  ohm. — (See  Ohm.) 

Unit  of  Acceleration.— (See  Acceleration,  Unit  of.) 

Unit  of  Activity.— (See  Activity,  Unit  of.) 

Unit  Differnce  of  Potential  or  Electro-Motive 
Force. — Such  a  difference  of  potential  between  two  points 
that  requires  the  expenditure  of  one  erg  of  work  to  bring  a 
unit  of  positive  electricity  from  one  of  these  points  to  the  other, 
against  the  electric  force.  (See  Erg.) 

Unit  Jar.— (See  Jar,  Unit.) 

Unit   of  Current,  Jacobi's A  current  which 

passed  through  a  voltameter  will  liberate  in  one  minute  a  cubic 
centimetre  of  oxygen  and  hydrogen  at  0°  C.  and  760  m.  m. 
barometric  pressure. 

1 

One  Jacobi's  Unit  of  Current  equals Weber  per  second. 

(Obsolete.) 

Unit  of  Heat,  New.— (See  Therm.) 

Unit  of  Mass.— (See  Mass,  Unit  of.) 

Unit  of  Power. — (See  Power,  Unit  of.) 

Unit  of  Pressure,  New —(See  Barad.) 

Unit  of  Resistance,  Jacobi's The  electric  re- 
sistance of  25  feet  of  a  certain  copper  wire  weighing  345  grains. 

Another  unit  of  electric  resistance  proposed  by  Jacobi  was 
the  resistance  of  a  copper  wire  one  metre  in  length  and  one 
millimetre  in  diameter. 

Unit  of  Resistance,  Matthiesscn's The  resist- 
ance of  one  statute  mile  of  pure  annealed  copper  wire  ^  of 
an  inch  in  diameter  at  15.6°  C. 


814  A  DICTIONARY  OF  ELECTRICAL 

Unit  of  Resistance,  Varley's The  resistance 

of  one  statute  mile  of  a  special  copper  wire  TJS  of  an  inch  in 
diameter. 

Varley's  unit  was  afterwards  adjusted  by  him  to  equal  25 
Siemens  mercury  units. 

Unit  of  Resistance.— Such  a  resistance  that  unit  dif- 
ference of  potential  is  required  to  cause  a  currant  of  unit 
strength  to  pass. 

Unit  Quantity  of  Electricity.— The  quantity  of  elec- 
tricity conveyed*  by  unit  current  per  second. 

Unit  of  Supply,  Electrical A  unit-provisionally 

adopted  in  England  by  the  Board  of  Trade,  equal  to  1,000 
amperes  flowing  for  one  hour  under  an  electro-motive  force 
of  one  volt. 

This  would,  of  course,  equal  1,000  watt  hours,  and  would 
be  the  same  as  100  amperes  flowing  for  ten  hours  under  one 
volt. 

One  unit  of  electrical  supply  is  equal  to  1.34  actual  horse 
power  expended  for  one  hour,  and  will  feed  13.4  Swan  lamps 
of  21  candle  power  for  one  hour.  It  is  equal  in  illuminating 
power  in  Swan  lamps,  to  the  light  produced  by  100  cubic  feet 
of  gas  consumed  in  twenty  14-candle  burners  in  one  hour. 

Unit  Strength  of  Current.— Such  a  strength  of  current 
that  when  passed  through  a  circuit  one  centimetre  in  length, 
arranged  in  an  arc  of  one  centimetre  radius,  will  exert  a 
force  of  one  dyne  on  a  unit  magnet  pole  placed  at  the 
centre. 

Unit  of  Velocity,  Wew The  Kine— (See  Kine.) 

Units   C.   G.   S. The  centimetre-gramme-second 

units. — (See  Units,  Fundamental.) 

Units,  Derived Various  units  obtained  or  derived 

from  the  fundamental  units  of  Length,  L,  Mass,  M,  and  Time,  T. 
The  derived  units  and  their  dimensions  are  as  follows  : 


WORDS,  TEEMS  AND  PHRASES.  615 

Area,  L2. — The  Square  Centimetre. 

Volume,  L3.— The  Cubic  Centimetre. 

Velocity,  V.— Unit  Distance  traversed  in  Unit  Time,  or  * 

L 

V=  —    -    (1) 
T 

Acceleration,  A. — The  rate  of  change  which  will  produce  a 
change  of  velocity  of  one  centimetre  per  second. 

V 

A  =  -    -    (2) 
T 

Substituting  in  equation  (2)  the  value  of  V  in  equation  (1), 
we  have, 

L 

T      L 

A  =  -  =  -    •    (3) 
T       T8 

1 

Force,  F. — The  Dyne,  or  the  force  required  to  act  on  unit 
mass  in  order  to  impart  to  it  unit  velocity. 

F  =  MxA    •    (4) 

Substituting  the  value  of  A  derived  from  equation  (2),  we 
have, 

V 

F=Mx- • 
T 

Substituting  the  value  of  V  derived  from  equation  (1),  we 
have, 

M     L       ML 

F=-x-= •    (5) 

T      T         T8 

Work  or  Energy,  W.— The  Erg,  or  the  work  done  in  over- 
coming  unit  force  through  unit  distance. 

ML             ML8 
W  =  FxL  = xL  = • 


16  A  blCTIONARY    OP  ELECTRICAL 

Power,  P.— The  Unit  Rate  of  Doing  Work* 
•  ML2 

W        T8       ML8 
P  =  -  = = (6) 

ip  ip  rpg 


Unit§,  Electro-Magnetic A  system  of  units 

derived  from  the  C.  G.  S.  units,  employed  m  electro-magnetic 
measurements.  , 


Units,  Electro-magnetic,  Dimensions  of 

f  ML 

Current  strength  =  Intensity  of  Field  x  Length  = 

T 


Quantity  =  Current  x  Time  =  |/M  x  L   . 

Potential.  Dif.  of  Pot.  )          Work  l/MxL' 

Electro-motive  force  C 


Resistance  = 


Quantity  T8 

Electro-motive  force        L 


Current  T 

Quantity       T2 

Capacity  = =  —   • 

Potential        L 

Units,  Electrostatic Units  based  on  the  force 

exerted  between  two  equal  quantities  of  electricity. 

Two  systems  of  electric  units  are  derived  from  the  C.  G.  S. 
system,  viz.,  the  Electrostatic  and  the  Electromagnetic.  These 
units  are  based  respectively  on  the  force  exerted  between  two 
quantities  of  electricity,  and  between  two  magnet  poles. 

The  electrostatic  units  embrace  the  units  of  Quantity, 
Potential,  and  Capacity.  No  particular  names  have  as  yet 
been  adopted  for  these  units. 

Unit  of  Quantity. — That  quantity  of  electricity  which  will 
repel  an  equal  quantity  of  the  same  kind  of  electricity  placed 


WORDS,  TERMS  AND  PHRASES.  617 

at  a  distance  of  one  centimetre  from  it  with  the  force  of  one 
dyne. 

Electrostatic  potential,  or  power  of  doing  electrostatic 
work,  is  measured  in  units  of  work,  or  ergs. 

Unit  Difference  of  Potential. — Such  a  difference  of  poten- 
tial between  two  points  as  requires  the  expenditure  of  one  erg 
of  work  to  bring  up  a  unit  of  positive  electricity  from  one 
point  to  the  other  against  the  electric  force. 

Unit  of  Capacity — Such  a  capacity  of  a  conductor  as  re- 
quires a  charge  of  one  unit  of  electricity  to  raise  it  to  unit 
potential. 

Specific  Inductive  Capacity.— The  ratio  between  the  induc- 
tive capacity  of  a  substance  and  that  of  air,  measured  under 
precisely  similar  conditions. 

The  specific  inductive  capacity  is  obtained  by  comparing  the 
capacity  of  a  condenser  filled  with  the  particular  substance, 
and  the  capacity  of  the  same  condenser  when  filled  with  air. 
The  specific  inductive  capacity  of  air  is  taken  as  unity. 

Units,  Electrostatic,  Dimensions  of.— 


Quantity  =   |/  force  x  (distance)2  =   |/  F  x  L8  =  — 


Quantity 
Current  = 


Time 
Work 


Potential  = 


Quantity  T  T 

Potential  T 

Resistance  = =  L  1  T  =  —    • 

Current  L 

Quantity 

Capacity  = =  L  . 

Potential 


618  A    DICTIONARY  OF   ELECTRICAL 

One  Quantity 

Specific  Inductive  Capacity  = =  A  simple 

Another  Quantity 
ratio  or  number. 

Force  ,     , 

Electro-motive  Intensity  = . =  M*  L*  T-1  = 

Quantity 

i/lfxL 


T 

The  fractional  and  negative  exponents  used  above  are 
merely  convenient  methods  of  expressing  the  contraction  of 
roots,  and  division  by  the  quantity  represented  by  the  nega- 
tive exponent. 

Unit§,  Fundamental The  units  of  length,  time, 

and  mass,  to  which  all  other  quantities  can  be  referred. 

The  unit  of  length  is  now  generally  taken  as  the  Centimetre  ; 
the  unit  of  time  as  the  Second  ;  and  the  unit  of  mass  as  the 
Gramme.  These  form  a  system  of  measurement  known  as 
the  centimetre-gramme-second  system,  or  the  C.  G.  S.  system, 
or  absolute  system. 

The  dimensions  of  the  fundamental  units,  are  designated 
thus: 

Length  =  L. 
Mass  =  M. 
Time  =  T. 

Unit§  of  Heat.— (See  Heat,  Units.) 

Units,  Magnetic. — Units  based  on  the  force  exerted  be- 
tween two  magnet  poles. 

Unit  Strength  of  Magnetic  Pole. — Such  magnetic  strength 
of  pole  that  repels  another  magnetic  pole  of  equal  strength 
placed  at  unit  distance  with  unit  force,  or  one  dyne. 

Magnetic  Potential— Power  of  doing  work  possessed  by  a 
magnet  pole. 

Magnetic  Potential  is  measured,  like  electrostatic  potential, 
in  units  of  work,  or  in  ergs. 


WORDS,  TERMS   AND  PHRASES.  61& 

Magnetic  Potential,  Unit  Difference  of.  —  Such  a  difference 
of  magnetic  potential  between  two  points  that  requires  the 
expenditure  of  one  erg  of  work  to  bring  up  a  magnetic  pole 
of  unit  strength  towards  a  like  pole. 

Unit  Intensity  of  Magnetic  Field.  —  Such  an  intensity  of 
magnetic  field  as  acts  on  a  north-seeking  pole  of  unit  strength 
with  the  force  of  one  dyne. 

Units,  Magnetic,   Dimensions  of  -- 


Strength  of  Pole  .or  >        ^  (Distance)  .  . 

antity  of  Magnetism  f  T 

Work  yiiTxL 

Magnetic  Potential  = 


Strength  of  pole 

Force 
Intensity  of  field  = 


Strength  of  pole         L8  x  T 

Units,  Practical  -  -  —  Multiples  or  fractions  of  the 
absolute  or  centimetre-gramme-second  units. 

The  practical  units  have  been  introduced  because  the  abso- 
lute units  are  either  too  small  or  too  large  for  actual  use. 

Electro-motive  Force.—  The  Volt  -  100,000,000  C.  G.  S.  or 
absolute  units,  that  is,  10  8  absolute  units  of  resistance.  (See 
Volt.) 

Resistance.—  The  Ohm  —  1,000,000,000  absolute  units  of  re- 
sistance, or  109  absolute  units.  (See  Ohm.) 

Current.—  The  Ampere  =  TV  Absolute  Unit  of  Current. 
(See  Ampere.) 

Quantity.—  The  Coulomb  =  TV  Absolute  Unit  of  Quantity, 
of  the  electro  magnetic  system.—  (See  Coulomb.) 
1 

Capacity.—  The  Farad  =  --  Absolute  Unit  of  Cap- 

1,000,000,000 
acity,  or  109  units  of  capacity.     (See  Farad.) 

Universal  Discharger.—  (See  Discharger,  Universal.) 


620  A  DICTIONARY  OP  ELECTRICAL 

Vacuum,  Absolute A  space  from  which  all 

traces  of  residual  gas  have  been  removed. 

A  term  sometimes  loosely  applied  to  a  high  vacuum.  It  is 
doubtful  whether  an  absolute  vacuum  is  attainable  by  any 
physical  means. 

Vacuum,  High Such  a  vacuum  that  the  length 

of  the  mean  free  path  of  the  molecules  of  the  residual  atmos- 
phere is  equal  to,  or  exceeds,  the  dimensions  of  the  containing 
vessel.  (See  Layer,  Crookes1.) 

Vacuum,  L.OW  or  Partial Such  a  vacuum 

that  the  mean  free  path  of  the  molecules  of  the  residual  gas 
is  small,  as  compared  with  the  dimensions  of  the  containing 
vessel.  (See  Tubes,  Geissler.) 

In  a  high  vacuum,  groups  of  molecules  can  move  across  the 
containing  vessel  without  meeting  other  groups  of  molecules. 
In  a  low  vacuum,  such  a  group  of  molecules  would  be  broken 
up  by  collision  against  other  groups  before  reaching  the 
other  side  of  the  vessel. 

Vacuum  Pumps.— (See  Pumps.) 

Vacuum  Tubes. — (See  Tubes,  Vacuum.) 

Valency. — The  worth  or  value  of  the  chemical  atoms  as 
regards  their  power  of  displacing  other  atoms  in  chemical 
compounds.  (See  Atomicity.) 

The  worth,  or  valency,  of  oxygen  is  twice  as  great  as  that  of 
hydrogen,  since  one  atom  of  oxygen  is  able  to  replace  two 
hydrogen  atoms  in  chemical  combinations. 

Valve-Burner,  Electric  Argand (See  Ar- 

gand  Valve-Burner,  Electric.) 

Valve,  Electric An  electrically  controlled  or 

operated  valve. 

In  systems  of  electro-pneumatic  signals,  gaseous  or  liquid 
pressure  controlled  by  electrically  operated  valves,  is  em- 
ployed to  move  signals,  ring  bells,  control  water  and  air 
valves,  or  to  perform  other  similar  work. 


WORDS,  TERMS  AND  PHRASES. 


621 


Vapor  Globe  of  Incandescent  Lamp.— A  glass 
globe  surrounding  the  chamber  of  an  incandescent  electric 
lamp,  for  the  purpose  of  enabling  the  lamp  to  be  safely  used 
in  explosive  atmospheres,  or  to 
permit  the  lamp  to  be  exposed  in 
places  where  water  is  liable  to 
fall  on  it 

Such  a  vapor  globe  is  shown  in 
Fig.  389. 

Variable  State  of  Charge 
of  Telegraph  JLine.  —  (See 
State,  Variable.) 

Variation,  Annual,  Diurn- 
al, Irregular,  Secular. 

— (See  Declination,  Magnetic,  Va- 
rieties of.) 

Variation  Chart.  —  (See 
Chart,  Variation.) 

Variation  Compass. — (See 
Compass,  Variation.) 

Variation  Needle.  —  (See 
Needle,  Declination.) 

Variations,  magnetic 

— (See  Magnetic  Variations.) 

Varnish,  Electric or 

Insulating  Varnish.— A  varn- 
ish formed  of  any  good  insulating 
material. 

Shellac  dissolved  in  alcohol,  applied  to  a  thoroughly  dried 
surface  and  afterwards  hardened  by  baking,  forms  an  excel- 
lent varnish. 

Vegetation,  Effects  of  Electricity  on Most 

vegetable  fibres  contract  on  the  passage  of  an  electric  cur- 
rent through  them  when  in  the  living  plant. 


622  A  DICTIONARY  OF  ELECTRICAL 

Velocity,  Angular (See  Angular  Velocity.) 

Velocity  of  Discharge.— The  time  required  for  the  pass- 
age of  a  discharge  through  a  conductor,  as  compared  with  its 
length. 

By  means  of  a  rapidly  revolving  mirror  Wheatstone  meas- 
ured the  velocity  at  which  the  discharge  of  aLeyden  jar  passed 
through  half  a  mile  of  copper  wire  as  288,000  miles  per  second. 

The  velocity  of  discharge  through  long  conductors  or  cables 
is  much  lessened  by  the  capacity  of  the  cable  and  the  effects 
of  induction,  etc.  (See  Retardation.) 

Velocity  Ratio.— A  remarkable  ratio,  in  the  nature  of  a 
velocity,  that  exists  between  the  ratio  of  the  electro-static  and 
the  electro-magnetic  values  of  the  electric  units. 

This  ratio  will  be  understood  from  the  comparison  of  the 
following  units : 

Mi  Ll  T- 
Quantity  = 


Mi  L* 
Here  the  value  of  the  ratio,  viz. ,  the  length  divided  by  the 

L 
time,  is  clearly  in  the  nature  of  a  velocity,  for  V  =  —    • 

T 
Mi  Li  T-i     T       1 

Potential  =  — j =—  =  —    • 

Mi  L*  T-»    L      V 

L  L8 

Capacity  = =  —  =  V»    • 

L-i  TS      T!S 

L-i  T     T2       1 

Resistance  = =  —  =  —    • 

L    T-1     L8     V8 

A  remarkable  similarity  exists  between  the  value  of  the 

velocity  expressed  in  C.  G.  S.  units,  and  the  velocity  of  light, 

which  is  of  great  significance  in  the  electro-magnetic  theory 

of  light.    (See  Light,  Electro-Magnetic  Theory  of.) 

The  velocity  of  light  is,  say,  2.9992  X  1010  centim.  per  second. 

The  velocity  ratio,  v,  is  2.9800  X  1010  centimetres  per  second. 


WORDS,  TERMS  AND  PHRASES.  623 

Ventilation  of  Armature.— Devices  for  the  free  pass- 
age of  air  or  other  fluid  through  the  armature  of  a  dynamo- 
electric  machine  in  order  to  prevent  its  over-heating.  (See 
Dynamo-Electric  Machine,  Armature,  Ventilation  of.) 

Vernier.— A  device  for  the  approximately  accurate 
measurement  of  smaller  differences  of  length  than  can  be 
readily  detected  by  the  eye. 

There  are  a  variety  of  vernier  scales  in  use. 

Vernier  Wire  Gauge.    (See  Wire  Gauge,  Vernier.) 

Vibration.— A  to-and-fro  motion  of  the  particles  of  an 
elastic  medium.  (See  Waves.) 

Vibrations,    Sympathetic (See    Sympathetic 

Vibrations.) 

Vis-Viva.— The  energy  stored  in  a  moving  body.     Hence, 
the  measure  of  the  amount  of  work  that  must  be  performed 
in  order  to  bring  a  moving  body  to  rest. 
M  V 

The  vis-viva  = • 

2 

This  term  is  gradually  becoming  obsolete. 

Vitreou§  Electricity.— A  term  formerly  employed  to 
indicate  positive  electricity. 

It  was  formerly  believed  that  the  friction  of  glass  with 
other  bodies  always  produced  positive  electricity. 

The  term  is  now  replaced  by  positive  electricity.  (See 
Resinous  Electricity.) 

Volcanic  Lightning.    (See  Lightning,  Volcanic.) 

Volt. — The  practical  unit  of  electrormotive  force. 

Such  an  electro-moti  ve  as  is  induced  in  a  conductor  which 
cuts  lines  of  magnetic  force  at  the  rate  of  100,000,000  per  sec. 

Such  an  electro-motive  force  as  would  cause  a  current  of 
one  ampere  to  flow  against  the  resistance  of  one  ohm. 

Such  an  electro-motive  force  as  would  charge  a  condenser  of 
the  capacity  of  one  farad  with  a  quantity  of  electricity  equal 
to  one  coulomb. 


634  A  DICTIONARY  OF  ELECTRICAL 

Volt-Ampere.— The  watt  or  unit  of  electric  power.  (See 
Power,  Electric.) 

Volt-Meter  Oalvanometer. — (See  Galvanometer,  Volt- 
Meter.) 

Voltaic  Alternatives.— (See  Alternatives,  Voltaic.) 
Voltaic  Arc.— (See  Arc,  Voltaic.) 
Voltaic  Battery.— (See  Battery,  Voltaic.) 

Voltaic  Cell.— An  electric  source  consisting  of  a  voltaic 
couple  and  one  of  two  electrolytes.  (See  Cell,  Voltaic.) 

Voltaic  Couple. — Two  dissimilar  metals,  or  a  metal  and 
a  metalloid,  capable  of  acting  as  an  electric  source,  when 
dipped  in  an  electrolyte,  or  capable  of  producing  a  difference 
of  electric  potential  by  mere  contact.  (See  Couple,  Voltaic.) 

Liquids  and  gases  are  capable  of  acting  as  voltaic  couples. 

Voltaic  Element.— One  of  the  two  substances  that  form 
a  voltaic  couple.  (See  Couple,  Voltaic.) 

Voltaic  Electricity.— Electricity  produced  by  the  agency 
of  a  voltaic  cell  or  battery. 

Electricity  is  the  same  thing,  or  phase  of  energy,  by  what- 
ever source  it  is  produced. 

Voltaic  or  Current  Induction.— A  variety  of  electro- 
dynamic  induction  produced  by  circuits  on  themselves,  or  in 
neighboring  circuits.  (See  Induction,  Electro-Dynamic.) 

Voltameter.— An  electrolytic  cell  employed  for  measuring 
the  strength  of  the  current  passing  through  it  by  the  amount 
of  chemical  decomposition  effected  in  a  given  time. 

Various  electrolytes  are  employed  in  voltameters,  such  as 
aqueous  solutions  of  sulphuric  acid,  copper  sulphate,  or  other 
metallic  salts. . 

In  the  water  voltameter  shown  in  Fig.  390,  the  battery 
terminals  are  connected  with  platinum  electrodes  immersed 
in  water  slightly  acidulated  with  sulphuric  acid,  and  placed 


WORDS,  TERMS  AND  PHRASES.  625 

inside  glass  tubes,  also  filled  with  acidulated  water.  On  the 
passage  of  the  current,  hydrogen  appears  at  the  kathode,  and 
oxygen  at  the  anode,  in  nearly  the  proportion  of  two  volumes 
to  one.  (See  Ozone.) 


Fig.  S90. 

In  the  case  of  sulphuric  acid  (hydrogen  sulphate)  the  decom- 
position would  appear  to  be  as  follows  : 

H8  S  04  =  H2  +  S04. 

The  hydrogen  appears  at  the  electro  negative  terminal,  or 
kathode.  The  SO4  appears  at  the  electro  positive  terminal  or 
anode,  but,  combines  with  one  molecule  of  water,  thus, 
SO4  +  H,  O  =  H,  SO4  4-  O,  gaseous  oxygen  being  given  off 
at  the  anode. 

Voltameters  are  not  as  well  suited  as  galvanometers  for  the 
measurement  of  electric  currents,  because  a  certain  electro- 
motive force  must  be  reached  before  electrolysis  is  effected. 

The  voltameter  in  reality  measures  the  coulombs,  and, 
therefore,  is  valuable  as  a  current  measurer  only  when  the 
current  is  constant. 

Coulomb-meter  would,  therefor,  be  the  preferable  term. 

Then,  again,  time  is  required  to  produce  the  results,  and 
considerable  difficulty  is  experienced  in  maintaining  the  cur- 


626  A  DICTIONARY  OF  ELECTRICAL 

rent  strength  constant,  either  on  account  of  variations  in  the 
electro-motive  force  of  the  source,  or  of  variations  in  the 
resistance  of  the  voltameter. 


Voltameter,  Siemens'  Differential 

— A  form  of  voltameter  employed  by  Sir  Wm.  Siemens  for  de- 
termining the  resistance  of  the  platinum  spiral  in  his  electric 
pyrometer.  (See  Pyrometer,  Electric. ) 

Two  separate  voltameter  tubes  provided  with  platinum 
electrodes  and  filled  with  dilute  sulphuric  acid,  are  provided 
with  carefully  graduated  tubes  to  determine  the  volume  of  the 
decomposed  gases.  (See  Voltameter. ) 

A  current  from  a  battery  is  divided  by  a  suitable  commu- 
tator into  two  circuits  connected  respectively  with  the  two 
voltameter  tubes.  In  one  of  these  circuits  a  known  resistance 
is  placed,  in  the  other  the  resistance  to  be  measured,  i.  e. ,  the 
platinum  coil  used  in  the  electric  pyrometer. 

Edison's  electric  meter  consists  of  a  V  oltameter.  (See  Meter, 
Electric.) 

Volt-ammeter. — A  variety  of  galvanometer  capable  of  di- 
rectly measuring  both  the  difference  of  potential  and  the  am- 
peres. 

Volt-Coulomb.— The  unit  of  electric  work.  The  Joule. 
(See  Joule.) 

Voltmeter. — A  galvanometer  for  measuring  the  electro- 
motive force,  or  difference  of  potential,  between  any  two 
points  in  a  circuit.  (See  Galvanometer.) 

Vulcanized  Fibre.— A  variety  of  insulating  material 
suitable  for  purposes  not  requiring  the  highest  insulation. 

Vulcanized  fibre  is,  however,  seriously  affected  by  long  ex 
posure  to  moisture. 

Vulcanite  or  Ebonite. — A  variety  of  vulcanized  rubber 
extensively  used  in  the  construction  of  electric  apparatus. 

Though  an  excellent  insulator,  vulcanite  will  lose  its  insu- 
lating properties  by  condensing  a  film  of  moisture  on  its  sur- 


WORDS,  TERMS  AND  PHRASES.  627 

face.  This  can  be  best  removed  by  the  careful  application  of 
heat. 

The  surface  is  very  liable  to  become  covered  by  a  film  of 
sulphuric  acid  due  to  the  gradual  oxidation  of  the  sulphur. 
Mere  friction  will  not  remove  this  film,  but  it  may  be  removed 
by  washing  with  distilled  water.  A  thick  coating  of  varnish 
will  obviate  this  last  defect. 

Watchman's  Electric  Register.— A  device  for  per- 
manently recording  the  time  of  a  watchman's  visit  to  each 
locality  he  is  required  to  visit  at  stated  intervals. 

These  registers  are  of  a  variety  of  forms.  They  consist,  how- 
ever, in  general,  of  a  drum  or  disc  of  paper  driven  by  clockwork, 
on  which  a  mark  is  made  by  a  stylus  or  pencil,  operated  by 
the  closing  of  a  circuit  by  a  push  button  pressed  or  key  turned 
by  the  watchman  at  each  station. 

Water  Battery.— (See  Battery,  Water.) 

Water  Dropping  Accumulator.—  (See  Accumulator, 

Water  Dropping.) 

Water,  Electrolysis  of The  decomposition  of 

water  by  the  passage  through  it  of  an  electric  current. 

When  pure,  water  does  not  appear  to  conduct  electricity ; 
it  is  therefore  not  quite  certain  that  pure  water  can  be  elec- 
trolytically  decomposed.  The  addition  of  a  small  quantity  of 
sulphuric  acid,  or  of  a  metallic  salt,  however,  renders  its  elec- 
trolysis readily  accomplished. 

Water-Level  Alarm.— (See  Alarm,  Liquid  Level.) 
Water  Pyrometer. — (See  Pyrometer,  Water.) 

Watches,    Demagnetization   of Pro- 

csesses  for  readily  removing  magnetism  from  watches. 

The  demagnetization  of  watches  can  be  readily  effected  by 
a  method  proposed  by  J.  J.  Wright.  The  watch  is  held  by 
its  chain  and  slowly  lowered  to  the  bottom  of  a  hollow 
conical  coil  of  wire,  and  then  slowly  withdrawn  from  the  coil. 


A  DICTIONARY   OF   ELECTRICAL 


The  wire  is  wound  on  the  coil,  as  shown  in  Fig.  391,  in 
the  shape  of  a  cone,  viz.,  with  a  single  turn  at  the  top,  and 
gradually  increasing  in  number  of  turns  towards  the  bottom. 

The  conical  coil  is  con- 
nected with  a  source  of 
rapidly  alternating  cur- 
rents. 

As  the  watch  is  low- 
ered in  the  coil,  it  be- 
comes gradually  mag- 
netized more  and  more 
powerfully  with  oppo- 
site polarities,  thus  com- 
pletely reversing  and 
removing  any  polarity  it 
previously  possessed.  As 
TA  \  it  is  now  slowly  raised 

V JTZ       Source   of  Alternating          I  f  rom  out  the  hollow  cone> 

y Current- J  this     magnetization    be- 
comes less  and  less,  until, 
if  removed  from  the  coni- 
cal coil  while  high  above  its  apex,  all  sensible  traces  of  mag- 
netism will  have  disappeared. 

Watt.— The  volt-ampere,  or  unit  of  electric  work.  (See 
Work,  Electric,  Unit  of.) 

Watt-Hour,  Watt-Minute,  Watt-Second.— Units  of 

work. 

Terms  employed  to  indicate  the  expenditure  of  an  electrical 
power  of  one  watt,  for  an  hour,  minute,  or  second. 

Watt-Meter. — A  galvanometer  by  means  of  which  the 
simultaneous  measurement  of  the  difference  of  potential  and 
the  current  passing  is  rendered  possible. 

The  Watt-Meter  consists  of  two  coils  of  insulated  wire,  one 
coarse  and  the  other  fine,  placed  at  right  angles  to  each  other 


WORDS,  TERMS  AND  PHRASES. 


629 


as  in  the  ohm-meter,  only  instead  of  the  currents  acting  on  a 
suspended  magnetic  needle,  they  act  on  each  other,  as  in  the 
electro-dynamometer. 

Waves,    Amplitude    of  -  —(See    Amplitude   of 

Waves.) 

Waves,  Electric (See  Oscillations,  Electric.) 


Waves  of  Condensation  and  Rarefaction.— The 

alternate  spheres  of  condensed  and  rarefied  air  by  means  of 
which  sound  is  transmitted.     (See  Sound  Waves.) 

Weber. — A  term  formerly  employed  for  the  unit  of  elec- 
tric current,  and  replaced  by  ampere.     (See  Ampere.) 


630  A  DICTIONARY  OF  ELECTRICAL 

Weber. — A  term  proposed  by  Clausius  and  Siemens  for  a 
magnetic  pole  of  unit  strength  but  not  adopted. 

This  same  term  was  also  employed  to  designate  the  unit 
strength  of  current.  Now  replaced  by  the  term  ampere. 

Weight,  Atomic  —        —(See  Atomic  Weight.) 

Weight,   Breaking of  Telegraph  Wires.— 

(See  Breaking  Weight  of  Telegraph  Wires.) 

Welding,  Electrie Effecting  the  welding  union 

of  metals  by  heatjof  an  electric  origin. 

In  the  process  of  Elihu  Thomson,  the  metals  are  heated  to 
electric  incandescence  by  currents  obtained  from  inverted 
induction  coils,  and  are  subsequently  pressed  or  hammered 
together. 

Fig.  392,  shows  the  Thomson  apparatus  for  the  Direct  System 
of  Electric  Welding.  The  dynamo  is  combined  with  the  weld- 
ing apparatus.  The  armature  contains  two  separate  wind- 
ings ;  one  of  fine  wire,  in  series  with  the  field  magnet  coils, 
and  another  of  very  low  resistance,  being  formed  of  a 
U-shaped  bars  of  copper.  No  commutation  is  used,  the  alter- 
nating currents  being  well  adapted  for  heating  purposes.  The 
terminals  of  these  poles  are,  therefore,  directly  connected  to 
the  clamps  that  hold  the  bar  to  the  welder. 

Fig.  393,  shows  the  apparatus  for  the  Thomson  Indirect 
System  of  Electric  Welding.  This  system  is  applicable  to 
heavy  work,  and  cases  where  more  than  one  welding  ma- 
chine is  operated  by  the  current  from  a  single  dynamo. 

In  this  case  a  high  tension  current  is  converted  into  the  large 
welding  current  employed  by  means  of  a  suitably  proportioned 
transformer. 

The  welding  process  is  the  same  in  either  system,  and  con- 
sists essentially  in  leading  the  welding  current  into  the  pieces 
to  be  united  near  their  points  of  junction  when  brought  into 
firm  end  contact.  As  the  current  is  lead  across  the  junction 
the  temperature  rises  sufficiently  to  soften  the  metal,,  when 


WORDS,  TERMS  AND  PHRASES. 


631 


the  pieces  are  firmly  pressed  together  by  the  motion  of  the 
clamps  or  holders. 

In  the  process  of  Benardos  and  Olzewski,  the  heat  of  the  vol- 
taic arc  is  employed  for  a  somewhat  similar  process. 
Wheatstone's  Balance.— (See  Balance,  Wheatstone's.) 

Wheel,  Barlow's  or  Sturgeon's (See 

Disc,  Faraday's.) 


Fig.  393. 

—See  Phonic  Wheel.) 

(See  Reaction  Wheel.) 

A  term  employed  to  indicate 

the  circular  direction  of  the  lines  of  magnetic  force  surround- 
ing a  conductor  conveying  an  electric  current.  See  Field 
Electro  Magnetic,) 


Wheel,  Phonic  — 
Wheel,  Reaction 
Whirl,  Electric 


A  DICTIONARY  OF   ELFCTRlCAL 


Whistle,    Automatic    Electric    Steam 


—A 


steam  whistle,  employed  on  foggy  days  in  some  systems  of  rail- 
way signals,  when  the  visual  signals  can  not  be  seen,  in  which 
the  passage  of  the  steam  through  the  whistle  is  automatically 
obtained  by  the  closing  of  an  electric  contact,  or  the  passage 
of  the  locomotive  over  a  certain  part  of  the  track. 

Wimshurst  Electrical  Machine.— A  form  of  convec- 
tion electric  machine  invented  by  Wimshurst. 

Like  the  Holtz  ma- 
chine, the  Wimshurst 
machine  is  a  convection 
induction  machine.  It 
is,  however,  more  effi- 
cient in  action,  and  will 
,  probably  soon  super- 
sede the  former  ma- 
chine. The  Wimshurst 
machine  consists  of  two 
shellac-varnished  glass 
plates,  that  are  rapidly 
rotated  in  opposite  di- 
rections. Thin  metal- 
lic strips  are  placed  on 
the  outside  of  each  of 
the  plates,  in  the  radial 
positions  shown  m  Fig,  894.  These  metal  strips  act  both  as 
inductors  and  carriers;  the  carrier  of  one  plate  acting  as  an 
inductor  to  the  other  plate- 
Two  curved  brass  rods,  terminating  in  fine  wire  brushes 
that  touch  the  plates,  are  placed  as  shown,  one  at  the  front  of 
the  plate,  and  one  at  the  back,  at  right  angles  to  each  other. 
Pairs  of  conductors,  connected  together,  provided  with  collect- 
ing points,  are  placed  diametrically  opposite  each  other,  as 
shown.  Sliding  conductors,  terminated  with  metallic  balls, 
are  provided  for  discharging  the  conductors.  Leyden  jars 


Fig.  39lt. 


WORDS,  TERMS  AND  PHRASES.  633 

the  inner  coatings  of  which  are  connected  with  the  two  dis- 
charging rods,  and  the  outer  coatings  together  may  be  em- 
ployed in  this  as  in  the  Holtz  machine. 

The  exact  action  of  this  machine  is  not  thoroughly  under- 
stood. 


Wind,  Electric 


—  The  convection  stream  of  air 


particles  produced  at  the  extremities  of  points  attached  to  the 
surface  of  charged,  insulated  conductors.  (See  Convection, 
Electric.  Flier,  Electric.) 


fig  305. 

Windage  of  Dynamo.—  A  term  proposed  for  the  air 
gap  between  the  armature  and  the  pole  pieces  of  a  dynamo. 

Winding,  Compound 

Dynanto-  Electric  Machine.) 

Windings,    Ampere  -  —{See    Turns,    Am- 

ptre.) 


(See  Compound  Wound 


634 


A  DICTIONARY  OF  ELECTRICAL 


Windings,  Bi-Filar  of  Coils.— (See  Bi-Filar 

Windings  of  Coils.) 

Wire  Gauge.— A  device  for  accurately  measuring  the 
diameter  of  a  wire. 

The  round  wire  gauge,  shown  in  Fig.  395,  is  very  generally 
used  for  telegraph  lines.  Notches  of  varying  widths,  cut  in 
the  edges  of  a  circular  plate  of  tempered  steel,  serve  to  ap- 
proximately measure  the  diameter  of  a  wire,  the  side  of  the 
wire  being  passed  through  the  slots.  Numbers,  indicating  the 
different  sizes  of  the  wire,  are  affixed  to  each  of  the  openings. 

Wire  Gauge j  Vernier  or  micrometer A 

gauge  employed  for  accurately  measuring  the  diameter  of 
a  wire  in  thousandths  of  an  inch,  based  on  the  principle  of 
the  vernier  or  micrometer.  See  Fig.  396. 

The  wire  to  be  measured  is 
placed  between  a  fixed  support 
B,  and  the  end  C,  of  a  long  mov- 
able screw,  which  accurately  fits 
a  threaded  tube  a.  A  thimble  D, 
provided  with  a  milled  head  fits 
over  the  screw  C,  and  is  attached 
to  the  upper  part.  The  lower  cir- 
Fig-  396.  cumference  of  D,  is  divided  into 

a  scale  of  20  equal  parts.  The  tube  a,  is  graduated  into 
divisions  equal  to  the  pitch  of  the  screw.  Every  fifth  of  these 
divisions  is  marked  as  a  larger  division. 

The  principle  of  the  operation  of  the  gauge  is  as  follows  : 
Suppose  the  screw  has  50  threads  to  the  inch,  the  pitch  of 
the  screw,  or  the  distance  between  two  contiguous  threads, 
is,  therefore,  T^»  or  -02  ojf  an  inch- 

One  complete  turn  of  the  screw  will  therefore  advance  the 
sleeve  D,  over  the  scale  a,  the  .02  inch.  If  the  screw  is  only 
moved  through  one  of  the  20  parts  marked  on  the  end  of  the 
thimble  or  sleeve  parts,  or  the  ^  of  a  complete  turn,  the  end 
C  advances  towards  B  the  ^of  jv,  i.  e.,  ^^  or  .001  inch. 


WORDS,  TERMS  AND  PHRASES.  635 

Suppose,  now,  a  wire  is  placed  between  B  and  C,  and  the 
screw  advanced  until  it  fairly  fills  the  space  between  them, 
and  the  reading  shows  two  of  the  larger  divisions  on  the  scale 
a,  three  of  the  smaller  ones,  and  three  on  the  end  of  the  sleeve 
D.  Then 

2  larger  divisions  of  scale  a =0.2  inch 

3  smaller  divisions  of  scale  u =    .06 

3  divisions  on  circular  scale  onD =    .006 

Diameter  of  wire =  0.266 

Serious  inconvenience  has  arisen  in  practice  from  the 
numerous  arbitrary  numbers  or  sizes  of  wires  employed  by 
different  manufacturers.  These  differences  are  gradually 
leading  to  the  abandonment  of  arbitrary  sizes  for  wires,  and 
employing  in  place  thereof,  the  diameters  directly  in  inches 
or  thousands  of  an  inch. 
\Virc,  Grounded (See  Ground  or  Earth.) 

Wire,  Insulated Wire  covered  with  any  insu- 
lating material. 

Cotton  and  silk  are  generally  employed  for  insulating  pur- 
poses, either  alone,  or  in  connection  with  various  gums,  resins, 
or  other  material*,  which  are  plastic  when  heated,  but  which 
solidify  on  cooling.  India  rubber,  caoutchouc,  and  various 
mixtures  and  compounds  are  also  employed  for  the  same 
purpose. 

For  most  of  the  purposes  of  line  wires,  high  insulating 
powers,  combined  with  a  low  specific  inductive  capacity,  is 
required  in  the  insulating  materials. 

For  overhead  wires  a  waterproof  covering  is  necessary.  In 
the  neighborhood  of  combustible  materials,  some  fireproof 
covering  is  desirable. 

Wires,    Conductibility  and    Sizes    of— . 

The  following  tables  give  the  resistance,  size,  weight  per 
foot,  etc.,  of  wire  according  to  some  of  the  principal  wire 
gauges. 


636 


A  DICTIONARY  OP  ELECTRICAL 


Number,  Diameter,    Weight,  Length,   and  Resistance  of 
Pure  Copper   Wire. 


AMERICAN    GAUGE. 


Diam. 

Weight 
Sp.  Gr.  -8.889. 

Length. 

Resistance  of  Pure  Copper 
at  70°  Fahrenheit. 

Lbs. 

Ohms 

Feet 

No. 

Inches. 

Grs.  per 
Ft 

per  1000 
feet. 

Ft,  per 
Lb. 

%r 

per 

Ohm. 

Ohms  per 
Lb. 

0000 

.460 

4475.33 

639.33 

1.56 

.051 

19605.69 

.0000798 

000 

.40964 

3549.07 

507.01 

1.97 

.064 

15547.87 

.000127 

00 

.36480 

2814.62 

402.09 

2.49 

.081 

1JS30.36 

.000202 

0 

.3-2495 

319.04 

3.13 

.102 

9783.63 

.000320 

1 

.28930 

1770J3 

252.88 

3.95 

.129 

7754.66 

.00051 

2 

.25763 

1403.79 

200.54 

4.99 

.163 

6149.78 

.000811 

3 

.22942 

1113.20 

159.03 

6.29 

.205 

4S76.73 

.001289 

4 

.20431 

882.85 

126.12 

7.93 

.259 

3867.62 

.00205 

5 

.18194 

700.10 

100.01 

10.00 

.326 

3067.06 

.00326 

6 

.16202 

555.20 

79.32 

12.61 

.411 

2432.22 

.00518 

7 

.14428 

440.27 

6290 

15.90 

.519 

1928.75 

.00824 

8 

.12849 

349.18 

49.88 

20.05 

.654 

1529.69 

.01311 

9 

.11443 

276.94 

39.56 

25.28 

.824 

1213.22 

.02083 

10 

.10189 

219.57 

31.37 

31.88 

1.040 

961.91 

.03314 

11 

.09074 

174.15 

24.88 

40.20 

1.311 

762.93 

.05269 

12 

.08081 

138.11 

19.73 

50.60 

1.653 

605.03 

.08377 

13 

.07196 

109.52 

15.65 

63.91 

2.084 

479.80 

.13321 

14 

.06108 

86.86 

12.41 

80.59 

2  628 

380.51 

.2118 

15 

.05706 

68.88 

9.84 

101.68 

3.314 

301.75 

.3368 

16 

.05082 

54.63 

7.81 

128.14 

4.179 

239.32 

.5S55 

17 

.045:25 

43.32 

6.19 

161.59 

5.269 

189.78 

.8515 

18 

040:50 

34.35 

4.91 

203.76 

6.645 

150.50 

1.3539 

19 

.03589 

26.49 

3.78 

264.26 

8.617 

116.05 

2.2772 

20 

.03196 

21.61 

3.09 

324.00 

10.566 

94.65 

3.423 

21 

.02846 

17.13 

2.45 

408.56 

13.323 

75.06 

5.443 

22 

.025347 

13.59 

1.94 

515.15 

16.799 

59.53 

8.654 

23 

.0*2571 

10.77 

1.54 

649.66 

21.185 

47.20 

13.763 

24 

.0*1 

8.54 

1.22 

819.21 

26.713 

37.43 

21.885 

25 

.0179 

6.78 

.97 

1032.96 

33.684 

29.69 

34.795 

26 

.01594 

5.37 

.77 

1302.61 

42.477 

23.54 

55.331 

27 

.014195 

4.26 

.61 

1642.55 

53.563 

18.68 

87.979 

28 

.01-2641 

3.38 

.48 

2071.22 

67.542 

14.81 

139.893 

29 

.011257 

2.68 

.38 

2611.82 

85.170 

11.74 

222.449 

30 

.010025 

2.13 

.30 

3293.97 

107.391 

9.31 

353.742 

31 

.008928 

1.69 

.24 

4152.22 

135.402 

7.39 

562.221 

32 

.00795 

1.34 

.19 

5236.66 

170.765 

5.86 

894.242 

33 

.00708 

1.06 

.15 

6602.71 

215.312 

4.64 

1421.646 

34 

.0063 

.84 

.12 

8328.30 

271.583 

3.68 

2261.82 

35 

.00561 

.67 

.10 

10501.35 

342.413 

2.92 

3596.104 

36 

.005 

.5:1 

.08 

13238.83 

431.712 

2.32 

5715.36 

37 

.00445 

.06 

16*91.01! 

544.287 

1.84 

9084.71 

38 

.(103965 

!34 

.05 

20854.fc5 

68ii.511 

1.46 

14320.26 

39 

.003531 

.27 

.04 

26302.23 

8K5  Oi6 

1.16 

22752.6 

40 

.003144 

.'21 

.03 

33175.14 

ioy:.8C5 

.92 

30223,60 

WORDS,  TERMS  AND   PHRASES. 


637 


Table  Showing  the  Difference  between   Wire    Gauges. 


London. 
.454 

Stubs. 
•454 

Brown  &  Sbarpe's. 
,    ,    .460 

.425 

,    ,    .425 

.40964 

.380 

,    ,    .380 

.36480 

.340 

.340 

.32495 

.300 

,    ,    .300 

.28930 

.284 

,   .284 

.25763 

.259 

.259 

.22942 

.238 

.238 

.20431 

.220 

,    .220 

.18194 

.203 

.203 

,    ,    .16202 

.180 

,    ,    .180 

.14428 

.165 

,    ,    .165 

.12849 

.148 

.148 

.11443 

.134 

.134 

.10189 

.120 

.120 

.09074 

.109 

.109 

.08081 

.095 

.095 

.07196 

.083 

.083 

.06408 

.072 

.072 

.05706 

.065 

.065 

.05082 

.058 

.058 

.04525 

.049 

.049 

.04030 

.040 

.042 

.03589 

.035 

.035 

.03196 

.0315 

,    .032 

,    ,    .02846 

.0295 

.028 

.025347 

.027 

.025 

.022571 

.025 

.022 

.0201 

.063 

.020 

.0179 

.0205 

.018 

.01594 

.01875 

.016 

.014195 

.0165 

,    ,    .014 

.012641 

.0155 

,    .013 

.011257 

.01375 

,    .012 

,    .010025 

.01225 

,    ,    .010 

,    ,    .00892N 

.01125 

.009 

.00795 

.01025 

.008 

.00708 

.0095 

.007 

.0063 

.009 

.005 

.00561 

.0075 

.004 

.005 

.0065 

f 

.00445 

.00575 

t 

.0089(5.-! 

.005 

t 

.003531 

.0045 

,    , 

.003144 

A  DICTIONARY  OF  ELECTRICAL 


NEW  LEGAL  STANDARD  WIRE  GAUGE  (ENGLISH). 

Tables  of  Sizes,  Weights,  Lengths  and  Breaking  Strains  of 
Iron  Wire. 


Size  on 
Wire 
Gauge. 

Diameter. 

Section- 
al area 
in  sq. 
inches. 

Weight  of 

Length 
Cwt. 

Breaking  strains 

Size 
on 
Wire 
Gauge 

Inch. 

Mille- 
metres. 

100 
yards. 

Mile. 

Anneal- 
ed. 

Bright 

Lbs. 

Lbs. 

Yards. 

Lbs. 

Lbs. 

7/0 

.500 

12.7 

.1963 

193.4 

3404 

58 

10470 

15700 

7/0 

6/0 

.464 

11.8 

.1691 

166.5 

2930 

67 

9017 

13525 

6/0 

5/0 

.432 

11.  ' 

.1466 

144.4 

2541 

78 

7814 

11725 

5/0 

4/0 

.400 

10.2 

.1257 

123.8 

2179 

91 

6702 

10052 

4/0 

3/0 

.372 

9.4 

.1087 

107.1 

1885 

105 

5796 

8694 

3/0 

2/0 

.348 

8.8 

.0951 

93.7 

1649 

120 

5072 

7608 

2/0 

1/0 

.324 

8.2 

.0824 

81.2 

1429 

138 

4397 

6595 

1/0 

1 

.300 

7.6 

.0707 

69.9 

1225 

161 

3770 

5655 

1 

2 

.276 

7. 

.0598 

58.9 

1037 

190 

3190 

4785 

2 

3 

.252 

6.4 

.0499 

49.1 

864 

228 

2660 

3990 

3 

4 

.232 

5.9 

.0423 

41.6 

732 

269 

2254 

3381 

4 

5 

.212 

5.4 

.0353 

34.8 

612 

322 

1883 

2824 

5 

6 

.192 

4.9 

.0290 

28.0 

502 

393 

1544 

2316 

6 

7 

.176 

4.5 

.0243 

24. 

422 

467 

1298 

1946 

7 

8 

.160 

4.1 

.0201 

19.8 

348 

566 

1072 

1608 

8 

9 

.144 

3.7 

.0163 

16. 

282 

700 

869 

1303 

9 

10 

.128 

3.3 

.0129 

12.7 

223 

882 

687 

1030 

10 

11 

.116 

3. 

.0106 

10.4 

183 

1077 

564 

845 

11 

12 

.104 

2.6 

.0085 

8.4 

148 

1333 

454 

680 

12 

13 

.092 

2.3 

.0066 

6.5 

114 

1723 

355 

532 

13 

14 

.080 

2. 

.0050 

5. 

88 

2240 

268 

402 

14 

15 

.072 

1.8 

.0041 

4. 

70 

2800 

218 

326 

15 

16 

.064 

1.6 

.0032 

3.2 

56 

3500 

172 

257 

16 

17 

.056 

1.4 

.0025 

2.4 

42 

4667 

131 

197 

17 

18 

.048 

1.2 

.0018 

1.8 

32 

6222 

97 

145 

18 

19 

.040 

1. 

.0013 

1.2 

21 

9333 

67 

100 

19 

20 

.036 

.9 

.0010 

1. 

18 

11200 

55 

82 

20 

(Issued  by  the  Iron  and  Steel  Wire  Mfrs.  Association.) 

Wires,  €ro§8 (See  Cross,  Electric.) 

Wires,  Crossing.    (See  Crossing  Wires.) 


WORDS,  TERMS  AND  PHRASES.  639 

Wood's  Button  Repeater.— (See  Repeater,  Tele- 
graphic.} 

Work,  Electric.— The  Joule.    (See  Joule.) 

Work,  Electric,  Unit  of The  volt-coulomb 

or  joule.     (See  Volt- Coulomb.  Joule.) 

Work,  Unit  of The  erg.    (See  Erg.) 

Yokes  of  Electro  Magnet.— The  solid  cross  pieces  of 
iron  that  join  the  ends  of  the  field  magnet  coils  of  dynamo  elec- 
tric machines,  or  of  electro  magnets  generally. 

Zero  methods.— (See  Null  Methods.) 

Zero  Potential.— The  potential  that  would  exist  at  an 
infinite  distance  from  any  electrified  body. 

In  practice,  the  potential  of  the  earth  is  regarded  as  the  zero 
potential.  (See  Potential,  Zero.) 

Zig-zag  Lightning.— Forked  lightning,  (See  Lightning, 
Zig-zag.) 

Zinc,  Amalgamation  of The  covering  or  amal- 
gamation of  zinc  with  a  layer  of  mercury. 

To  amalgamate  a  plate  of  zinc,  its  surface  is  first  thoroughly 
cleaned  by  immersing  the  plate  in  dilute  sulphuric  acid  of 
about  one  part  of  acid  to  ten  or  twelve  parts  of  water,  A  few 
drops  of  mercury  are  then  rubbed  over  its  surface,  thus  coat- 
ing it  with  a  bright  metallic  film  of  zinc  amalgam.  Care  must 
be  taken  not  to  use  too  much  mercury,  since  the  zinc  plate  will 
thus  be  rendered  brittle. 

The  necessity  for  amalgamating  the  zinc  arises  from  the 
loss  of  energy  through  local  action,  on  ordinary  plates. 

The  action  of  the  amalgam  appears  to  be  to  cover  the  sur- 
face of  the  zinc  plate  with  a  layer  of  chemically  pure  zinc. 
On  the  polarization  of  the  battery  on  closing  its  circuit  the  zinc 
ends  of  the  zinc-amalgam  are  turned  towards  the  negative 
plate,  thus  in  effect  producing  a  plate  of  chemically  pure  zinc. 


640  A  DICTIONARY  OF  ELECTRICAL,  ETC. 

Zincode  of  Voltaic  Cell.— A  term  formerly  employed 
to  indicate  the  zinc  terminal  or  electrode  of  a  voltaic  cell. 

The  negative  electrode  or  kathode,  are  preferable  terms. 

Zone,  Polar A  term  proposed  by  De  Watteville 

for  the  zone  or  region  surrounding  the  therapeutic  electrode 
applied  to  the  human  body  for  electric  treatment. 

Zone,  Peripolar A  term  proposed  by  De  Watte- 
ville for  the  zone  or  region  surrounding  the  polar  zone  on  the 
body  of  a  patient  under  electro  therapeutic  treatment. 

Zinc  Sender. — A  device  employed  in  telegraphic  cir- 
cuits, in  which,  in  order  to  counteract  the  retardation  pro- 
duced by  the  charge  given  to  the  line,  a  momentary  reverse 
current  is  sent  into  the  line  after  each  signal. 

A  zinc  sender  generally  consists  of  a  low  resistance  Siemens 
relay  introduced  between  the  line  and  the  front  contact  of  the 
signaling  key. 


APPENDIX. 


Balance   or   Neutral-Wire  Ampere   Meter.— An 

ampere  meter  placed  in  the  circuit  of  the  neutral  wire,  in  a 
three-wire  system  of  electric  distribution,  for  the  purpose  of 
showing  tl.e  excess  of  current  passing  over  one  side  of  the 
system  as  compared  with  the  other  side,  when  the  central 
wire  is  no  longer  neutral. 

Balanced  Metallic  Circuit.— A  metallic  circuit,  the 
two  sides  of  which  have  similar  electrical  properties. 

Banked  Battery. — (See  Battery,  Banked.} 

Battery,  Banked.— A  term  sometimes  applied  to  a  bat- 
tery from  which  a  number  of  separate  circuits  are  supplied 
with  current. 

The  term,  banked  battery,  is  sometimes  applied  to  a  multi- 
ple-arc connected  battery. 

Bed-Piece  of  Dynamo  Electric  Machine.— The 
frame  on  which  a  dynamo  is  supported. 

The  bed-piece  is  sometimes  called  the  dynamo  frame. 

Bell,  Night. (See  Night  Bell.) 

Board,  Cross-Connecting. (See  Cross  Con- 
necting Board.) 

Box,  Cable. (See  Cable  Box.) 

Box,  Junction. (See  Junction  Box.) 

Branch. — A  term  applied  to  any  principal  distributing 
conductor  from  which  outlets  are  taken,  or  taps  made. 

Break-Down  Switch.— A  special  switch,  employed  in 
small  three- wire  systems,  for  connecting  the  positive  and  nega- 
tive bus-wires  in  such  a  manner  as  to  permit  the  system  to 
be  supplied  with  current  from  the  dynamo  in  use  on  one  side 
of  the  system  only. 


2  APPENDIX. 

Bridges.— Heavy  copper  wires  suitably  shaped  for  connect- 
ing the  dynamo  electric  machines  in  a  station  to  the  bus-rods 
or  wires. 

Bug.— A  term  originally  limited  to  quadruplex  telegraphy 
to  designate  any  fault  in  the  operation  of  the  apparatus. 

This  term  is  now  employed,  to  a  limited  extent,  for  faults 
in  the  operation  of  electric  apparatus  in  general. 

Bug-Trap.— Any  device  employed  to  overcome  the 
"bug"  in  quadruplex  telegraphy. 

Bus-Rods  or  Wires. — Heavy  copper  rods  employed  in  a 
station,  to  which  all  the  generating  dynamos  are  connected 
and  from  which  the  current  passes  to  the  different  points  of 
the  distribution  system  over  the  feeders. 

Cable  Box.— A  receptacle  provided  for  holding  and  secur- 
ing the  terminals  of  a  cable,  or  underground  conductor. 

Cable  Laid-Up  in  Layers.— A  term  applied  to  a  cable, 
all  the  wires  of  which  are  in  layers. 

Cable  Laid-Up  in  Reversed  Layers.— A  term  ap- 
plied to  a  cable  in  which  the  conductors,  in  alternate  layers, 
are  twisted  in  opposite  directions. 

Cable  Laid-Up  in  Twisted  Pairs.— A  term  applied 
to  a  cable  in  which  every  pair  of  wires  is  twisted  together. 

Calling-Drop.— An  annunciator  drop  employed  to  indi- 
cate to  the  operator  in  a  telegraphic  or  telephonic  system 
that  one  subscriber  wishes  to  be  connected  with  another. 

Calling-Wire.— A  wire  employed  in  a  telegraphic  or 
telephonic  system,  by  means  of  which  a  subscriber  communi- 
cates with  the  central  office,  or  one  central  office  communi- 
cates with  another. 

Cam,  Listening. (See  Listening  Cam.) 

Capacity  of  a  Cable.— The  electrostatic  capacity  of 
one  conductor  of  a  <:able  as  compared  with  the  capacity  of  the 
remainder  of  the  conductors  grounded. 


Centre  of  Distribution.— In  a  system  of  multiple-distri- 
bution, a  place  where  branch  cut-outs  and  switches  are  placed 
in  order  to  control  communication  therewith. 

Climbers  and  Straps. — Devices  employed  by  linemen 
for  climbing  wooden  telegraph  poles. 

Colombin.— A  name  applied  to  the  insulator  between  the 
parallel  carbons  of  the  Jablochkoff  candle,  consisting  of  a 
mixture  of  sulphate  of  barytes  and  sulphate  of  lime. 

Commutating  Transformers,  Distribution  by 

(See  System  of  Electrical  Distribution  by  Commu- 

tating  Transformers.) 

Condensers,  system  of  Alternate  Current  Distri- 
bution by  Means  of (See  System  of  Alternate 

Current  Distribution  by  Means  of  Condensers.) 

Condensers,  System  of  Continuous  Current  Dis- 
tribution by  Means  of (See  System  of  Continu- 
ous Current  Distribution  by  Means  of  Condensers.) 

Contraplex  Telegraphy.— A  name  given  to  a  special 
system  of  duplex  telegraphjr. 

Cross  Arm. — A  horizontal  beam  attached  to  a  pole  for  the 
support  of  telegraph,  electric  light  and  other  electric  wires. 

Cross  Connecting  Board.— In  a  system  of  telegraphic 
or  telephonic  communication,  a  board  to  which  the  line  ter- 
minals are  run  before  entering  the  switchboard,  so  as  to 
readily  place  any  subscriber  on  any  desired  section  of  the 
switchboard. 

Cross  Connection,  Telephonic A  device  em- 
ployed in  systems  of  telephonic  communication  for  the  pur- 
pose of  lessening  the  bad  effects  of  induction,  in  which  equal 
lengths  of  adjacent  parallel  wires  are  alternately  crossed  so 
as  to  alternately  occupy  the  opposite  sides  of  the  circuit. 

Cross-Talk.— In  tplephony  an  indistinctness  in  the  speech 
transmitted  over  any  circuit  due  to  this  circuit  receiving, 


APPENDIX. 

either  by  accidental  contacts  or  by  induction,  the  speech 
transmitted  over  neighboring  circuits. 

Curb,  Double (See  Double  Curb.) 

Curb  Signaling. — In  cable  telegraphy  a  system  for  avoid- 
ing the  effects  of  retardation  by  rapidly  discharging  the  cable 
before  another  electric  impulse  is  sent  into  it,  not  by  connect- 
ing it  to  earth,  but  by  reversing  the  battery  and  then  connect- 
ing to  earth  before  beginning  the  next  signal. 

Curb  Signaling,  Double  Curb In  curb  signal- 
ing, a  method  by  which  the  cable,  after  connection  with  the 
battery  for  sending  a  signal,  is  subjected  to  a  reverse  battery, 
but  instead  of  being  put  to  earth  after  this  connection  as  in 
single  curb  signaling,  the  battery  is  again  reversed  and  con- 
nected to  earth. 

The  time  during  which  the  cable  is  connected  to  the  re- 
versed battery  before  being  put  to  earth,  that  is,  the  time 
during  which  it  receives  the  positive  and  negative  currents 
may  be  made  of  any  suitable  duration. 

Curb  Signaling,  Single  Curb In  curb  signaling, 

a  method  by  which  the  cable  after  connection  with  the  battery 
for  sending  a  signal,  is  subjected  to  a  reverse  battery  current 
and  then  put  to  earth  before  again  being  connected  to  the 
battery  for  sending  the  next  signal. 

Cut-out,  Duplex (See  Duplex  Cut-out.) 

Decalescence.— A  term  proposed  by  Prof.  Elihu  Thom- 
son for  the  absorption  of  sensible  heat  which  occurs  at  a  cer- 
tain point  during  the  heating  of  a  bar  of  steel. 

Decalescence  will  thus  be  observed  to  be  the  reverse  of 
recalescence,  which  is  the  phenomenon  of  the  emission  of 
sensible  heat  at  a  certain  point  during  the  cooling  of  a  heated 
bar  of  steel.  (See  Recalescence.) 

Distribution  of  Continuous  Currents  by  Means 
of  Condensers. — (See  System  of  Continuous  Current 
Distribution  by  Means  of  Condensers.) 


APPENDIX.  5 

Double  Curb.— AH  instrument  invented  by  Sir  William 
Thomson,  employed  in  curb  signaling,  by  means  of  which  the 
signals  are  made  and  the  curb,  either  single  or  double,  in  any 
required  proportion,  is  applied  automatically. 

Double  Curb  Signaling.—  (See  Curb  Signaling, 
Double  Curb.) 

Double  Plug.— A  plug  so  constructed  that  when  in- 
serted in  a  spring-jack  it  makes  two  connections,  one  at  its 
point  and  one  at  its  shank.  (See  Spring  Jack.) 

Double  Trolley  System  of  Electric  Railroad*.— 
A  system  of  electric  railroad  propulsion,  in  which  a  double 
trolley  is  employed  to  take  the  the  driving  current  from  the 
overhead  wires. 

The  double  trolley  system  differs  from  the  single  trolley 
system  in  that  it  employs  no  earth  return.  The  parallel 
wires  also  avoid  the  effects  of  injurious  induction  in  neighbor- 
ing telegraph  or  telephone  wires. 

Duplex  Cut-out.— A  cut-out  so  arranged  that  when  one 
box  is  fused  or  melted  by  an  abnormal  current,  another  can 
be  immediately  substituted  for  it. 

Electric  Thermo  Call.— An  instrument  for  sounding 
an  alarm  when  the  temperature  rises  above,  or  falls  below,  a 
fixed  point. 

In  one  form  of  this  instrument  a  needle  is  moved  over  a  dial 
by  a  simple  thermic  device  and  rings  a  bell  when  the  tempera- 
ture for  which  it  has  been  set  is  attained.  The  thermo-call 
is  applicable  to  the  regulation  of  the  temperature  of  dwell- 
ings, incubators,  hot  houses,  breweries,  drying  rooms,  etc. 

Feeder. — One  of  the  conducting  wires  or  channels 
through  which  the  current  is  distributed  to  the  main  con- 
ductors. 

Feeder-Switch. — The  switch  employed  for  connecting 
or  disconnecting  each  conductor  of  a  feeder  from  the  bus-bars 
in  a  central  station. 


6  APPENDIX. 

Feeder-Equalizer.—  An  adjustable  resistance  placed 
in  the  circuit  of  a  feeder  for  the  purpose  of  regulating  the 
difference  of  potential  at  the  junction  box. 

Fire  Balls. — A  term  sometimes  applied  to  globular  light- 
ning. (See Lightning,  Globular.) 

Force  de  Cheval.— The  French  term  for  horse  power. 
The  force  de  cheval  is  equal  to  32,560  foot  pounds  per  minute. 

Frame   of  Dynamo  Electric   machine.— The  bed 

piece  that  supports  a  dynamo  electric  machine. 

The  frame  is  sometimes  called  the  dynamo  bed  piece. 

Graduators.— Devices,  generally  electro  magnets,  in- 
serted in  a  circuit  so  as  to  obtain  the  makes  and  breaks, 
required  in  a  system  of  telegraphy,  so  gradually  that  they 
fail  to  influence  the  diaphragm  of  a  telephone  placed  in  the 
same  circuit,  and  thus  to  permit  a  simultaneous  telegraphic 
and  telephonic  transmission  over  the  same  wire. 

Ground  Detector. — In  a  system  of  incandescent  lamp 
distribution,  a  device,  placed  in  the  central  station,  for  show- 
ing by  the  candle  power  of  a  lamp,  the  proximate  location 
of  a  ground  on  the  system. 

Horse  Power  of  Water.— The  Indian  Government's 
term  for  horse  power  developed  by  falling  water. 

The  estimate  is  made  by  the  following  simple  rule  :  15  cubic 
feet  of  water  falling  per  second  through  one  foot  equals  1 
horse  power. 

House  IVIain. — A  term  employed  in  a  system  of  multiple 
incandescent  lamp  distribution  for  the  conductor  connecting 
the  house  service  conductors  with  a  centre  of  distribution. 

House-Service  Conductor.— A  term  employed  in  a 
system  of  multiple  incandescent  lamp  distribution  for  that 
portion  of  the  circuit  which  is  included  between  the  service 
cut-out  and  the  centre  or  centres  of  distribution,  or  between 
this  cut-out  and  one  or  more  points  on  house  mains. 


Hysteresis. — Molecular  friction  to  magnetic  change  of 
stress. 

That  property  of  a  medium  in  virtue  of  which  work  is  done 
in  changing  the  direction  or  intensity  of  magnetic  force  among 
its  parts. 

Intercrossing.— In  a  system  of  telephonic  communica- 
tion, a  device  for  avoiding  the  disturbing  effects  of  induction 
by  alternately  crossing  equal  sections  of  the  line.  (See  Cross- 
Connections,  Telephonic.) 

Joint,  Sleeve. —      •  —(See  Sleeve  Joint.) 

Junction  Box. — A  moisture-proof  box  provided  in  a 
system  of  underground  conductors  to  receive  the  terminals  of 
the  feeders,  and  in  which  connection  is  made  between  the 
feeders  and  the  mains  from  which  the  current  is  distributed  to 
the  individual  consumer. 

Kinetic  Theory  of  Matter.— A  theory  which  assumes 
that  the  molecules  of  matter  are  in  a  constant  state  of  motion 
or  vibration  towards,  or  from,  one  another. 

Applying  the  kinetic  theory  of  matter  to  gases,  the  mole- 
cules of  which  have  great  freedom  of  motion,  the  mol°- 
cules  are  so  far  removed  from  one  another  as  to  be  but  little, 
if  any,  influenced  by  their  mutual  attractions.  They  are 
therefore  assumed  to  move  in  straight  lines  with  very  great 
velocity  until  they  collide  against  one  another,  or  against  the 
sides  of  the  containing  vessel,  when  they  are  reflected  and 
again  run  in  straight  lines  in  a  new  path. 

Leg. — In  a  system  of  telephonic  exchange,  a  single  wire, 
where  a  ground  system  is  used,  or  two  wires  where  a  metallic 
circuit  is  employed,  for  connecting  a  subscriber  with  the  main 
switchboard,  by  means  of  which  the  subscriber  may  be  legged 
or  placed  directly  in  circuit  with  two  or  more  parties. 

Legging  Key-Board.— A  key-board  employed  for  the 
purpose  of  legging  an  operator  into  the  circuit  connecting  two 
or  more  subscribers. 


8  APPENDIX. 

Line§,  Overhead. (See  Overhead  Lines.) 

Listening  Cam.— In  a  telephonic  exchange  system  a 
metallic  cam  by  means  of  which  the  operator  is  placed  in  cir- 
cuit with  a  subscriber. 

main  Feeder.— (See  Standard  or  Main  Feeder.) 

Main.  House (See  House  Main,) 

HIain§,  Street (See  Street  Mains.) 

matter,    Kinetic    Theory    of (See    Kinetic 

Theory  of  Matter.) 

Motor-Generators.  —  Dynamo-electric  generators  in 
which  the  power  required  to  drive  the  dynamo  is  obtained 
from  an  electric  current. 

Motor  generators  are  used  in  systems  of  electrical  distribu- 
tion for  the  purpose  of  changing  the  potential  of  the  current. 
They  consist  of  dynamos,  the  armatures  of  which  are  furnished 
with  two  separate  windings,  of  fine  and  of  coarse  wire  respect- 
ively. One  of  these,  generally  the  fine  wire,  receives  the 
driving  or  motor  current,  usually  of  high  potential,  and  the 
other,  the  coarse  wire,  furnishes  the  current  used,  usually  of 
low  potential. 

motor-Generators,  System  of  Electric  Distribu- 
tion by (See  System  of  Electric  Distribution  by 

Motor-  Generators. ) 

Neutral  Relay  Armature.— A  term  applied  in  contra- 
distinction to  a  polarized  relay  armature,  in  which  the  relay 
armature,  consisting  of  a  piece  of  soft  iron  wire,  closes  a  local 
circuit  whenever  its  electro-magnet  receives  an  impulse  over 
the  main  line.  (See  Polarized  Armature.) 

Neutral  Wire.— The  middle  wire  of  a  three-wire  system 
of  electric  distribution. 

Night  Bell.— In  a  telephone  exchange,  a  bell  switched 
into  connection  with  the  shunted  circuit  of  an  annunciator 


APPENDIX.  0 

case,  and  provided  for  calling  the  attention  of  the  night 
operator  by  its  constant  ringing  to  the  falling  of  a  drop. 

Outlet.— In  a  system  of  incandescent  lamp  distribution  the 
point  of  attachment  for  a  socket  in  a  fixture. 

Overhead  L,ine.— A  term  applied  to  telegraph,  tele- 
phone, and  electric  light  or  power  lines  that  run  overhead,  in 
contradistinction  to  similar  lines  placed  underground. 

Phantom  Wire§.— A  term  applied  to  the  additional  cir- 
cuits or  wires  obtained  in  any  single  wire  or  conductor  by  the 
use  of  some  multiplex  telegraphic  system.  (See  Telegraphy, 
Multiplex.  Synchronous  Multiplex  System  of  Telegraphy.) 

Phoiioplrx  Telegraphy. — A  system  of  telegraphic 
transmission  in  which  pulsatory  currents,  superposed  on  the 
ordinary  Morse  currents,  actuate  a  modified  telephonic  re- 
ceiver, and  thus  permit  the  simultaneous  transmission  of 
several  separate  messages  over  a  single  wire  without  inter- 
ference. 

Platymeter. — An  instrument  invented  by  Sir  William 
Thomson  for  comparing  the  capacities  of  two  condensers. 

Plugs. — Metallic  connections  in  the  shape  of  plugs  for 
making  or  breaking  circuits  by  placing  them  in,  or  removing 
them  from,  metallic  sockets  connected  with  the  circuits  to  be 
made  or  broken. 

Plugging. — Completing  a  circuit  by  means  of  plugs. 

Recale§cence.— The  property,  first  pointed  out  by  Bar- 
rett, possessed  by  steel  when  cooling  after  being  heated  to  in- 
candescence, of  again  becoming  incandescent  after  a  certain 
degree  of  cooling  has  been  effected. 

A  steel  wire  heated  at  the  middle  or  near  one  end  to  a 
bright  red,  and  allowed  to  cool  in  a  dim  light,  will  be  ob- 
served to  cool  until  a  low  red  heat  is  reached,  when  it  will  be 
observed  to  reheat  at  some  point  in  the  originally  heated  por- 
tion. This  re-heating  is  manifested  by  a  brighter  red  spot 


10  APPENDIX. 

which  moves  along  the  portion  originally  heated.  This  reheat- 
ing is  called  recalescence,  and  is  due  to  latent  heat  (potential 
energy)  which,  disappearing  when  the  bar  was  heated,  again 
becomes  sensible  (kinetic  energy)  on  cooling-. 

The  temperature  at  which  recalescence  takes  place  is 
sensibly  the  temperature  at  which  heated  steel  regains  its 
magnetizability. 

Relay  Armature,  Neutral (See  Neutral  Relay 

Armature.) 

Service    Conductor,    House (See    House 

Service  Conductor.) 

Service,  Street (See  Street  Service.) 

Single  Curb  Signaling.— (See  Curb  Signaling,  Single 
Curb.) 

Sleeve  Joint. — A  method  of  joining  conducting  wires  by 
passing  them  through  tubes  and  then  twisting  and  soldering. 

Stackling  a  "Wire. — Placing  an  insulator  between  the 
two  ends  of  a  cut  wire. 

Standard  or  Alain  Feeder.— The  main  feeder  to  which 
the  standard  pressure  indicator  is  connected,  and  whose  pres- 
sure controls  the  pressure  at  the  ends  of  all  the  other  feeders. 

The  term  pressure  in  the  above  definition  is  used  in  the 
sense  of  electro-motive  force  or  difference  of  potential. 

Street  Mains. — In  a  system  of  incandescent  lamp  distri- 
bution the  conductors  through  which  the  current  is  distri- 
buted from  the  feeder  ends,  through  cut-outs,  to  the  district  to 
be  lighted,  and  from  which  service  wires  are  taken. 

Street  Service. — In  a  system  of  incandescent  lamp  distri- 
bution that  portion  of  the  circuit  which  is  included  between 
the  main  and  the  service  cut-out. 

Switch,  Break  Down (See  Break  Down 

Switch.) 


APPENDIX.  11 

System  of  Alternate  Current  Distribution  by 
II can*  of  Condensers.— A  system  of  alternate  current 
distribution  in  which  condensers  are  employed  to  transform 
current  charges  of  high  potential  received  from  an  alternat- 
ing current  dynamo,  to  charges  of  low  potential  which  are 
fed  to  the  lamps  or  other  electro-receptive  devices. 

In  the  system  of  McElroy  the  conversion  from  high  to  low 
potential  is  obtained  by  making  the  plates  of  the  condensers 
charged  by  the  dynamo,  or  primary  plates,  smaller  than  the 
secondary  plates,  the  ratio  of  the  area  of  the  primary  plates 
to  that  of  the  secondary  plates  being  made  in  accordance  with 
the  ratio  of  conversion  desired. 

System  of  Continuous  Current  Distribution  by 
Tic  MI*  of  Condensers.— A  system  of  distribution  devised 
by  Doubrava  in  which  a  continuous  current  is  conducted  to 
certain  points  in  the  line  where  a  device  called  a  "disjunctor" 
is  employed  to  reverse  it  periodically  and  the  reversed 
currents  so  obtained  directly  used  to  charge  condensers  in  the 
circuit  of  which  induction  coils  are  placed. 

The  condensers  are  used  to  feed  incandescent  lamps  or  other 
electro-receptive  devices. 

System  of  Electrical  Distribution  by  Commuta- 
I  ing  Trail sforniers. — A  system  of  electrical  distribution 
in  which  motor-generators  are  used,  but  neither  the  armature 
nor  the  field  magnets  are  revolved,  a  special  commutator 
being  employed  to  change  the  polarity  of  the  magnetic 
circuits. 

System  of  Electric  Distribution  by  Motor- 
Oenerators. — A  system  of  electric  distribution  in  which  a 
continuous  current  of  high  potential,  distributed  over  a  main 
line,  is  employed  at  the  points  where  its  electric  energy  is  to 
be  utilized  for  driving  a  motor,  which  in  turn  drives  a  dynamo, 
the  current  of  which  is  used  to  energize  the  electro-receptive 
devices. 


12  APPENDIX. 

In  another  system  of  motor-generators  the  motor  and 
dynamo  are  combined  in  one  machine  with  a  double  wound 
armature,  the  fine  wire  coils  in  which  receives  the  high 
potential  driving  current  and  the  coarse  wire  coils  furnish  the 
low  potential  current  used  in  the  distribution  circuits. 

System  of  Simultaneous  Telegraphy  and  Tele- 
phony over  a  Single  Wire.— A  system  for  the  simul- 
taneous transmission  of  telegraphic  and  telephonic  messages 
over  a  single  wire. 

These  systems  are  based,  in  general,  on  the  fact  that  a 
gradual  make  and  break  in  a  telephone  circuit  fails  to  appreci- 
ably affect  a  telephone  diaphragm.  By  the  use  of  graduators 
the  makes  and  breaks  required  for  the  transmission  of  the  tele- 
graphic dispatch  are  effected  so  gradually  that  they  fail  to 
appreciably  influence  the  telephone  diaphragm  and  thus  per- 
mit simultaneous  telegraphic  and  telephonic  transmission  over 
a  single  wire.  (See  Graduators.) 

Tailings. — False  markings  received  in  systems  of  auto- 
matic telegraphy,  due  to  retardation. 

Telegraphy,  Contraplex (See  Contraplex 

Telegraphy.") 

Telegraphy,  Phonoplex — (See  Phonoplex 

Telegraphy.) 

Thermo  Call,  Electric (See  Electric  Thermo 

Call.) 

Thermolysis.— A  term  applied  to  the  chemical  decom- 
position of  a  substance  by  heat. 

Thermolysis,  or  dissociation,  is  an  effect  produced  by  the 
action  of  heat  somewhat  similiar  to  the  effect  of  electrolysis, 
or  chemical  decomposition  produced  by  the  passage  of  an 
electric  current.  When  a  chemical  substance  is  heated,  the 
vibration  of  its  molecules  is  attended  by  an  inter-atomic 
vibration  of  its  constituent  atoms  so  that  a  decomposition 
ensues.  If  the  temperature  is  not  excessive  these  liberated 


APPENDIX.  13 

atoms  recombine  with  others  which  they  meet,  but  at  higher 
temperatures  such  recombination  is  impossible  and  a  perma- 
nent decomposition  ensues,  called  thermolysis  or  dissociation. 

Torque. — The  stress  on  a  shaft  due  to  electro-magnetic 
action,  that  is,  the  turning  effort  exerted  by  the  armature  of 
a  motor,  for  instance,  under  the  influence  of  the  current. 

The  torque  is  usually  measured  in  pounds  of  pull  at  the  end 
of  a  radius  or  arm  1  foot  in  length. 

Transposing.— In  a  system  of  telephonic  communication 
a  device  for  avoiding  the  bad  effects  of  induction  by  alter- 
nately crossing  equal  consecutive  sections  of  the  line.  (See 
Cross- Connection,  Telephonic.) 

Trolley  System,  Double for  Electric  Rail- 
roads.—(See  Double  Trolley  System  of  Electric  Railroads. 

Trunk  Lines. — In  a  system  of  telephonic  communica- 
tion lines  connecting  distant  stations  and  used  by  a  number 
of  subscribers  at  each  end  for  purposes  of  intercommunication. 

Trunkiiig  Switchboard.— A  switchboard  in  which  a 
few  subscribers  only  are  connected  with  the  operator,  thus 
enabling  him  to  obtain  any  other  subscriber  by  means  of 
trunk  wires  extending  to  the  other  sections. 

Unit§  and  Terms,  Proposed  IVew The  fol- 
lowing units  and  terms  have  recently  been  proposed  by  Oliver 
Heaviside,  but  have  not  been  generally  accepted  or  adopted. 
These  definitions  are  given  in  Mr.  Heaviside's  language. 

"Conductance.— Capacity  for  conducting  electricity. 

"Numerically,  the  ratio,  in  absolute  measure,  of  the  current 
strength  to  the  total  electro-motive  force  in  a  circuit  of  uni- 
form flow.  A  quantity  with  the  nature  of  a  slowness  or  re- 
ciprocal to  a  velocity.  The  practical  unit  is  called  the  mho." 

"Conductivity. — Conductance  per  unit  volume." 

"Elaxtance. — Capacity  of  a  dielectric  for  opposing  electric 
charge  or  displacement. 


14  APPENDIX. 

"Numerically,  the  ratio,  in  absolute  measure,  of  the  differ- 
ence of  potential  in  an  electrostatic  circuit  to  the  total  charge 
or  displacement  therein  produced.  The  reciprocal  of  per- 
mittance and  a  quantity  of  the  inverse  nature  of  a  length." 

"Elastivity.— Elastance  per  unit  volume  of  dielectric." 

"Impedance. — Capacity  for  opposing  the  variable  flow  of 
electricity. 

"  Numerically,  in  the  absolute  measure,  the  ratio  of  the  total 
electro-motive  force  to  the  current  strength  at  any  instant  in 
a  circuit  of  variable  flow.  A  quantity  with  the  nature  of  a 
velocity  and  in  any  circuit  always  greater  than  the  resistance." 

"Inductance. — Capacity  for  magnetic  induction. 

"  Numerically,  in  absolute  measure,  the  number  of  unit  lines 
of  magnetic  force  linked  with  a  circuit  traversed  by  the  unit 
current  strength.  Sometimes  alluded  to  as  the  coefficient  of 
self  induction.  A  quantity  of  the  nature  of  a  length." 

"Inductivity. — Specific  capacity  for  magnetic  induction. 

"  The  numerical  ratio  of  the  induction  in  a  medium  to  the 
induction  producing  it." 

"Permittance.— Electrostatic  capacity.  Capacity  of  a  dielec- 
tric for  assisting  charge  or  displacement. 

"Numerically,  the  ratio,  in  absolute  measure,  of  the  total 
charge  or  displacement  in  an  electrostatic  circuit,  to  the  dif- 
ference of  potential  producing  it.  A  quantity  with  the  nature 
of  a  length." 

"Permittivity. — The  numerical  ratio  of  the  permittance  of 
a  dielectric  to  that  of  air. 

"Also  known  as  specific  inductive  capacity." 

"Reluctance. — Capacity  for  opposing  magnetic  induction. 

"Numerically,  the  ratio,  in  absolute  measure,  of  the  magneto- 
motive force  in  a  magnetic  circuit  to  the  total  induction  therein 
produced.  A  quantity  with  the  nature  of  the  reciprocal  of  a 
length.  Sometimes  described  as  magnetic  resistance." 


APPENDIX.  15 

"Reluctancy  or  Reluctivity.— Reluctance  per  unit  volume. 

"Sometimes  described  as  specific  magnetic  resistance.  A 
numeric,  the  reciprocal  of  inductivity." 

''Resistance.— Capacity  for  opposing  the  steady  flow  of 
electricity. 

"Numerically,  in  absolute  measure,  the  ratio  of  the  total 
electro-motive  force  to  the  current  strength  in  a  circuit  of 
uniform  flow.  A  quantity  with  the  nature  of  a  velocity.  The 
practical  unit  is  called  the  ohm." 

"Resistivity. — Resistance  per  unit  volume  ;  sometimes 
alluded  to  as  specific  resistance." 

Wire,  Neutral  —        —(See  Neutral  Wire.) 

Wires,  Phantom (See  Phantom  Wires.) 


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